I'm getting really tired of my hair (big ol' 3c frizzy mess) and I'm trying to familiarize myself with Keratin treatments because I read that it doesn't damage/causes minimal damage to your hair. The thing is I'm really confused about what Keratin treatments really are and what they do because there seem to be many types. I was hoping someone could help me answer a few questions.

1. What does keratin do exactly?
2. Is it permanent? If not, how long does it last, and does your hair revert back to its original state?
3. Does it straighten your hair completely or can you choose how you want it to look? I have 3c hair and I would like looser curls, not straight hair.
4. Does Keratin damage your hair?
5. Do Keratin conditioning treatments (like shampoos/conditioners with keratin as an ingredient) give you the same results as the ones you get in a salon?
6. Have you tried any Keratin treatments, and were you satisfied? If so, which treatments would you recommend?

Thanks, guys!