Hey, I'm 17 and underweight but I have a sprain on my left chest area above my breast and below my shoulder. How do you take care of it in that area?

RICE. Rest, Ice, Compression, Elevation. You can't really do compression to your chest, and it's always elevated except while sleeping. You can take NSAID's (ibuprofen, naproxen, etc.) to help with pain and inflammation. Time will heal most strains/sprains.