Hi Sus. Protein treatments (pt's) are intensive protein packed deep treatments you put on your hair for a specific amount of time to give it a big dose of protein all at once. Some pt's have a good amount of moisture in them as well, while others are mostly protein.
Protein is what gives hair structure and strength, while moisture gives it elasticity. You need a balance of both for happy hair. Too much moisture will leave you with limp, mushy feeling curls, while too much protein can leave you with dry, straw-like hair.
The easiest thing to do is maintain a balance with your daily products, but sometimes, a big dose of protein or moisture is needed to restore that balance. Protein treatments remedy overmoisturized /overconditioned hair, while deep moisture (dt's) help remedy overproteined hair.
I suggest reading this blog entry, by RedCelticCurls, about how to evaluate whether your hair needs moisture or protein, or is at a good balance point. It even has pics, which helped me out. Do follow the "excellent article" link too. It has in depth info. on evaluating moisture /protein needs.
There's always an exception to "the rules", but as for the basics...
Fine hair (small individual strands) needs protein.
Medium hair needs a balance of moisture and protein.
Coarse hair (large individual strands) needs moisture.
High porosity hair needs protein.
Medium porosity hair needs a balance.
Low porosity hair needs moisture.
You don't mention your hair properties (porosity, texture), but those are a good place to start in figuring out what your hair needs and what products will work for you. This page was a good reference for me. If you decide you need a pt after figuring out your hair properties and evaluating your hair, I suggest reading through this thread, by Rymorg2 (a stylist who posts here on nc.com), about how to do pt's. Lastly, this post has links to several threads concerning protein.