Im boy of 19. i started having beard from 17. but until now it is patchy beard not a full mans beard. how do i get rid of this patchy beard and how can i get normal beard??

Wait a few years and it will either fill in or not. If you don't like it now consider shaving for a couple years until your age brings out the potential Then grow it out. I know of no supplements/meds that are helpful in this process.

That your genetics speaking ! Make pattern baldness on the scalp can be modified with minoxidil spray, but I doubt tha would have a significant effect on facial hair - see a dermatologist for any possible new therapies and for more information