Welcome to the world of chickens!
Telling chickens apart can be difficult if they are the same breed. I have struggled with that too. The more time you spend with them, the easier it is to tell the differences in comb, legs, feathering, ect. However, changes can occur in the feathers or comb that make it hard to know who is who. Tagging or putting colored leg-bands on will allow you to tell them apart. However, with Red-stars, they often have different shades of color or patterns and can be told apart. For example, I have two red stars and one is far darker with less white on her then the other so her name is Maroon while the other one is called Pearl.
Other then that, I mostly just try to get as many different colors and breeds as possible so I can tell them apart. I have around 50 chickens right now and each one has a name. Remembering it isn't always easy, but I know each one's individual personality and appearance because I can tell them apart. In the past I had multiple leghorns, redstars and RIRs so it was far more difficult to do so.
This is one of my two Pearls (I can't tell them apart) in a nest box with Liberty my Barred Rock. I now only have one Pearl
This is Eowyn, a Red Star mix who is slightly lighter then her sister
Maroon is one of Dominator (our roosters) favorite hens. She is darker then my other Red Stars with fuller feathers and a shorter, broader tail.