How to do know if a chick is a female or a male??

I'm wondering if you can tell if a chicken a female or male? And what is the easiest and best way

The answer to this would depend on the breed(s) and ages of the birds. There are many ways to determine gender of a chick/chicken.
With newly hatched birds you can tell by a process known as "vent sexing" which is examination of the internal genital structure to determine if the bird is male or female -- it is not as straightforward as, say, a human infant, so there is an error rate of up to 15% even with the most experienced sexers. this is an image that can help to show what you would see and why it is not always that clear (males left, females right):


There are also certain characteristics that can be used to create "sex links" - which are a cross breeding that takes advantage of characteristics that are linked to the gender of the bird. This results in chicks that hatch with differences that make it possible to tell male from female at hatch - differences in color of the down, pattern of the down, leg color, feather development of the wing feathers in the first three days, etc. The pictures below show black and red sex links as chicks and as adults - you can see how they are easily differentiated.





Additionally, there are some breeds which are "auto sexing" - unlike sex links, these are not crossbred birds, but are actual breeds that are mated to the same breed and result in chicks that are able to be sexed at hatch because males and females have differences in color/pattern.

As birds age you can start to see differences in the comb/wattle development and color as early as 2-6 weeks which can help to indicate gender. Some breeds look similar as chicks but feather in with different patterns between male and female birds, making it possible to tell gender as soon as they begin to feather (3-5 weeks) -

Ultimately, at 12-16 weeks and beyond there are differences in the feathering between males and females for most breeds (there are some breeds in which males are "hen feathered", meaning these differences do not develop) -- these differences are illustrated here (hen top, roo bottom):

The EASIEST way is that males combs will turn RED while female combs will remain pink UNTIL point of lay between 5 to 6 months old or more with some breeds. So basically the female comb remains pink until she's ready to lay eggs. The male comb turns Red much more quickly. So if you have a 3 month old with a red comb it's probably male. Hope this helps.

There are many nuances to sexing young chickens. Age, breed, and origin are just a few factors that influence the nuances; they are not universal and may vary from breed to breed or even within the same breed from hatchery stock to breeder stock.

The most important thing about sexing is that you are not looking at one characteristic - you are looking at a group of characteristics to determine the big picture.

Most breeds can be sexed with accuracy at 8-12 weeks of age. "Most breeds", in this context, refers to common hatchery stock egg laying fowl; Production Reds, Buff Orps, Barred Rocks, New Hampshires, and so on. Other breeds may take significantly less or more time - for example, OEGBs and Seramas can often be easily sexed at 4-6 weeks of age; Silkies, on the other hand, cannot be sexed until 5-7 months of age and even then it's usually either a crow or an egg which determines the gender.

I sex based off a set list of characteristics: comb/wattles; size; feet; feathers; voice; stance; color; and personality. All of these are helpful, but only feathers are 100% accurate.

The easiest and most accurate characteristic to sex is the comb and wattles. In most breeds, cockerels will have significantly larger and brighter combs and wattles, while those of a pullet the same age should remain smaller and pink or yellow until they reach point of lay.

Size is an important factor to consider; cockerels will often be physically larger than their female siblings.

The saddle and wing bow feathers of cockerels are the only 100% accurate way to sex; as males grow, they will develop long, shiny, pointy feathers on the shoulders and saddle. They will also develop long, curved sickle feathers, but these come in a few weeks after saddle feathers; though sometimes the main tail feathers of a cockerel may be hooked at the end as a precursor to his developing sickles. Once a bird has developed saddle or wing bow feathers, you can be certain it is a cockerel*. A pullet, on the other hand, will retain short, round cushion and wing bow feathers. In most breeds, saddle feathers begins to develop between 8-12 weeks of age.

Voice is something to look at as well. While pullets will retain their soft, chirpy chick voice for quite a while, cockerels will often begin to have a rasp to their voice starting at 8-10 weeks of age, sometimes younger. Occasionally a cock will crow this young, another certain indicator of a cockerel, but this is rare.

Stance should be considered when sexing. Cockerels will stand taller and more alert, with their tails sticking up higher than a pullet's of the same breed.

Color, on some breeds, can also help when sexing. Cockerels of many breeds will be more colorful than their pullet counterparts; and in certain color patterns, namely Wheaten, Duckwing, and Partridge birds, dimorphic color patterns oftenbegin to develop as young as 4 weeks, with cockerels developing dark or black breast and females brown, salmon, or white.

Personality is, in my opinion, the least accurate of sexing characteristics, but worth a mention nonetheless. You may find that cockerels can be more friendly or bold than pullets of the same breed; some may be more aggressive, but honestly I've seen so many agressive and picky pullet chicks that I wouldn't really judge on aggression.

Also worth mentioning; vent sexing and sex linked or Autosexing fowl.

Vent sexing is the method practiced by commercial hatcheries. It allows chicks to be sexed with 90-98% accuracy at one day of age. It is, however, a very difficult art to learn. It involves looking into the vent of a day old chick to check for a "nodule" present in most cockerels, and many beginners find it not only near impossible to find said nodule, but also may even injure the chicks during the process due to their inexperience.

Sex links and Autosexing breeds are another facet of the quest to make sexing chickens easier, and in my opinion the most successful. They are created using our knowledge of genetics; certain genes are "sex linked", meaning they are found on the sex chromosome rather than regular autosomal chromosomes. Chickens (and other birds) are genetically the opposite of humans (and other mammals) in the sense that while in our species females are XX (homogametic) and males are XY (heterogametic), in chickens it is flipped and females are ZW while males are ZZ. This means that when it comes to sex linked genes, females can have only one while males are capable of carrying two copies. And as such, when females carrying a copy of one of these genes is bred to a male who carries no copies, she is only able to pass the gene down to her sons; her daughters recieve zero copies. And thus is produced a sex link; chicks are sexable at one day of age by their down color. The two most common sex link genes are Barring and Silver; these are used to create Black and Red sex links, respectively. Essentially, a male who's color won't interfere with the chick down (usually a red, such as an RIR, is used) is crossed over a female who is either Barred or Silver (example Barred Rock or Delaware). Sex links are usually hybrids, but two color patterns within the same breed could be used to create a mixed variety but pure breed sex link, example Partridge Rock over Barred Rock. There are also Autosexing breeds; these work off a similar principle as sex linked birds, except with the aim of being able to breed true; while sex link X sex link would not produce sex links, Autosexing X Autosexing will produce Autosexing. Autosexing focuses on the Barring gene, but rather than trying to sex based on the difference between males with one copy and females with no copy, they are sexed based on the difference between males with two copies and females with one copy.

Thanks for your help!