I don't know what your options are. Different feed stores stock different things. Also, I'm not sure what your goals are. I'll assume chickens that will become a laying flock. Meat birds are different.
A standard feed regimen is a starter for the first 6 weeks or so. This usually has 20 to 22% protein. Then from 6 weeks until 20 weeks or they start to lay, switch to a 16% grower. At 20 weeks or first egg, switch to 16% layer. There are minor differences in the composition of grower and layer, but the only significant difference is calcium for the egg shells. A lot of calcium is not good for growing chicks. It can cause bone deformation or kidney problems. Once they are grown it is not a big deal, but avoid excess calcium when they are chicks.
The idea is that they need a big boost of protein when they are starting out. They are doing a lot of growing and they are growing their first set of feathers. After they are fully feathered at about 5 weeks, their need to grow fast slows down. They need to mature their internal organs while they are growing, so they don't need to grow too fast if they are going to be layers.
Not everything is available everywhere. I can normally only get a combined Starter/Grower, about 20% protein if I remember right. You can feed this combined Starter/Grower from day 1 until you switch to layer. I can get a combined Grower/Finisher which is 15% protein. This is recommended from week 13 until they start to lay in place of the Grower. Again, just to slow them down a bit and let their body mature as they grow. You will also see different feeds that are higher in protein. 20% Flock Raiser, for example, is for flocks that are intended to be combined meat/egg laying flocks. This 20% Flock Raiser is not as high in protein as the feed intended for meat birds but is a good compromise. Some feeds are quite a bit higher in protein, but these are intended for game birds. You will see that chickens are not mentioned on the cover.
You may notice there are no real hard and fast, you have to do it this way and only this way, rules (except for the calcium). Chickens are pretty adaptable. The normal recommendation (often on the feed bag cover) is Starter for 6 weeks, then grower until they are ready for the extra calcium in layer. I don't do that because I don't have that option where I shop. I normally feed the combined starter/grower until I can switch to the developer. By this time they are free ranging anyway. Then I normally feed the entire flock 15% developer with oyster shell on the side until they are all ready for layer. If I could get 16% grower, I'd use that but it is not an option for me.
To further confuse it, you do not have to immediately switch over from starter to grower at 6 or 8 weeks, whichever you decide as your standard. Keep feeding whatever you have until it is gone. The 6 to 8 weeks is a range, not an absolute.
Also, the longer you store feed, the more nutrition it will lose. I would not over-buy to start with until you get a feel for how much they will eat. As they get older they will eat more. I recommend storing it in a metal trash can with a fairly tight fitting lid to keep it dry and the mice out.
Here is a comparison of the make-up of certain feeds, which shows that grower and layer are not that different except for the calcium.
16% Layer 15% Grower/ Flock Raiser
Finisher
Protein 16 15 20
Lysine 0.7 0.65 0.95
Methionine 0.35 0.29 0.35
Crude Fat 2.5 2.7 3.5
Crude Fiber 7 5 5
Min Calcium 3.8 0.6 0.8
Max Calcium 4.8 1.1 1.3
Phosphorus 0.5 o.6 0.7
Min Salt 0.25 0.2 0.35
Max Salt 0.75 0.4 0.85
I don't know if this helps or just confuses you. Good luck. It's really not that hard.