if you have fine hair, then protein treatments are good on a regular basis. medium texture like some protein, not a lot. so sometimes what is in other products is enough, or a very occasional protein treatment is good. if your texture is coarse, then stay away from protein.
you buy protein treatments just like you buy deep conditioners. there are many different brands and many can be bought locally. the one i use is curl junkie repair me which i buy on aveyou.com.
you really need to learn about hair properties before you start buying products/doing treatments, it will save you time and effort and money in the long run.