I am 20 years old, what should I do about my hair? (photos)

Fortunately, you supplied just barely enough of a view of your hair in the two most important areas (front and crown) to show that you have thinning in both areas. You have a strong forelock in the center of your thinning frontal area and this forelock may stay even if the hair around it disappears.  The best treatment at your age with this condition is the drug finasteride which may reverse it at your age. Also look at this post for more direction:  https://baldingblog.com/haircheck-test-how-it-is-done-video/