Hello! Welcome to Chickens!! So many of the choices you make will depend a lot on your unique set-up (climate, yard/coop set-up, flock mix, goals, etc.). With feeding, people tend to have pretty strong opinions about what is "best" to do but I think it's always best to educate yourself and then decide what works for what you have and need.
Most people have food available 24/7 for their birds and let them eat at-will. I would say that the most common set-up is to have your food and water in your run rather than in your coop, but you want to try to keep it in a place that is easy access for the chickens but NOT easy access for mice, sparrows, and other pests and where it will stay clean and dry. Depending on your set up you may want to consider having two separate feeders and waters to prevent bullying--this comes in handy if you plan on introducing new birds regularly.
Nipples are great for keeping the water clean and spill-free. I use a small float waterer rather than a nipple. It is somewhat similar to this:
http://www.amazon.com/Automatic-Waterer-Drinker-Chicken-Poultry/dp/B00EVVGUOO
Chickens are omnivores so meat scraps and insects are perfectly fine. You might also find that your birds catch bugs, and small mice, frogs, even snakes from time to time and chow down. I even give my birds left over chicken -- this is a little controversial to some I guess but eating muscle meat will not hurt them.
There is a pretty good treat chart in the learning center with come general dos and don'ts:
https://www.backyardchickens.com/a/chicken-treat-chart-the-best-treats-for-backyard-chickens
Most house food scraps are going to be fine. Veggies, meat, bread, pasta. Keep in mind that things like white bread that aren't healthy for you also aren't healthy for them so consider these snacks and treats and not all the time things. I would say scraps are fine as often as you want as long as it stays a small percentage of their overall diet--maybe 10-20%--it does not have to be exact. If you want to feed lots of scraps or grow fodder or something like that then perhaps consider a high protein feed for balance (see below).
For actual feed you have options. Here is a general break down of what you are likely to find at your feed store and what each is:
The most common progression is to do either 1. medicated started until 8 weeks or so, then a grower until laying age (5-7 months) and then a layer or 2. non-medicated starter until laying age then layer. I talk about other options below or 3. avoid layer and do flock raiser + oyster shell
These are types of feeding, means that the ingredients in the bag are different.
MEDICATED STARTER - This feed for baby birds and baby birds ONLY. It has a high protein for growing bodies and also has Amprolium which is a medication that is used to help prevent cocci (a parasite). This is OPTIONAL. Some people use it and some people do not. I would recommend reading about it and deciding what works for you. I personally do not use this.
NON-MEDICATED CHICK STARTER - This is chicken feed with higher protein and no extra calcium. Is is generally for young birds but because it not medicated it can also be fed to fixed-age flocks or to older birds if you want a higher protein feed.
GROWER (also FLOCK RAISER)- This is feed for adolescent birds or for adults depending on how you use it. It has less protein than a starter but does not have any extra calcium like a layer, meaning it is fine to eat for young birds and babies. If you are feeding it to laying birds you need to give them calcium on the side -- oyster shell (which you can buy at the feed store and looks like grey flakes) is the most common. The benefit is that the birds can regular their own calcium intake. This feeding method of Grower plus calcium is common for people with fixed flocks that have any non-laying or infrequently laying birds (roosters, young birds, sick birds, molting birds, etc.) If the calcium is separate the birds that do not need it won't eat it. This is the feeding method that I use.
LAYER - This is feed for LAYING hens only and is made to be complete nutrition for birds that are laying frequently. It has a normal adult amount of protein and extra calcium for egg shell production. Benefit is that everything you need comes in one bag. It is cheap and easy and you don't have to buy extra things if you don't want to. Downside is that any non-laying birds eating it will get too much calcium. Do NOT feed to young birds.
You can also get into organic feeds if you are interested in that. They are harder to find but it is possible to get organic feeds and also corn-free and soy-free feeds. Read your food bags to see what is inside and compare.
Chicken feed comes in different forms. These are just how the food is "packaged" basically and not the ingredients. For example, Layer crumble and Layer mash likely have the same basic stuff, they just physically look different.
Here is a good image of the different forms of feed. People usually pick one over the other because of waste and spillage and the type of feeder they have:
http://www.extension.org/pages/65936/crumbles#.U72nQo1dWgs
Some other things at your feed store that are snacks or extras:
OYSTER SHELL - This is calcium. If you are feeding layer you probably don't need it.
GRIT - This is little rocks (literally). If your chickens are outside all day and dig in the dirt then you do not need to buy this. If they are confined in a small area then it's a good idea. They eat these little rocks which collect in their gizzard and are used like teeth to grind up food. Grit is not a calcium source and oyster shell is not grit. These are commonly confused.
SCRATCH - This is a chicken snack (NOT a feed) and is usually mostly cracked corn. The idea is to toss it on the ground and let the chickens "scratch" around for it.
MEALWORMS - you can buy them dried or alive. Chickens LOVE them. If you want a very healthy protein snack you can farm them at home very easily. Good info in the learning center about this.
Ask lots of questions! Good luck!
