if you click the optifine thing that downloads when you download it, there are two options: install and extract
if you extract it's used as a mod like any other
if you install it give you it's own installation profile
future reference,
I looked up some things and found out that I had to click on the download to extract it using java, i guess? idk but i had to click on it, which I didn't know since it has a java icon. Anyway, then you put it in the mods folder and THEN it shows up in your mods list