What should i do with my hair?

I have a natural thick and wavy hair which is very frizzy when it's dried. It is also very brittle, break-edge and damaged. However, when i was a kid my hair used to be smooth, wavy (but not frizzy) and silky but when i started to reach my puberty, my hair started to frizz up and the volume increased around 3 times...i always put my hair into a bun to avoid exposing it until my friends ask me why don't i do some other styles, they told me that i should try blow drying my hair or straighten it but i seriously have no idea how to blow dry it, i mean i tried several times but i totally failed and i once had my hair permanently straighten (i did it 5 years ago) but because my face is round, it made my face looks even rounder and fatter. My another friend told me to get my hair relaxed but i seriously don't have any idea what it meant by 'to get your hair relaxed' and i wonder if it would damage my hair even more... what else could i do instead of relaxing my hair? which product should i use? and which style should i do?