What kind of coolant do I use in a 2007 Chevrolet Cobalt?

50 / 50 anti freeze to water is the old standard. Check the owner's manual or the antifreeze container. In Northern States in the winter time the proportions will change due to the VERY COLD weather. In the Southern states, it may remain the same. Antifreeze helps prevent rust and crud from forming also. It is a lubricant in a way and keeps the coolant from overheating quickly.

And... your car came equipped with GM's Dexcool. Use only Dexcool and water in your system. You cannot mix other types of antifreeze with it. Apparently it will clog the system. Read the labels carefully to make sure you have the right one.

How do I know if mine takes a different antifreeze I didn't have none in it and it don't have the manual so do I have to use that dextron or can I just use regular antifreeze

If its a Cobalt it uses dextron. They all do. It might even say so on the filler cap under the hood, but even if it doesn't, use dextron or something that says dextron compatible. Read the label on the jug before you buy it. It will clearly tell you what it is or what it works with.

Ooops. And I've been calling it dextron like you did, but its actually called Dex Cool. Use the right name or you'll end up with transmission fluid!

I have a cobalt and have peak in it right now just drained my old and didn’t have dex cool but buddy had peak he is also a mechanic and said it doesn’t matter what coolant you use they are all the same

I don't think your buddy knows what he's talking about. There is a difference and they are not compatible with each other. However there are some coolants out there that work with either one. The Peak product you are using may be compatible with both, but to say they are the same across the board is not correct. Guaranteed your car has Dex Cool in it because they all do. To fill it use Dex Cool or something that says on the label it can be used with either.