Welcome 
Get some proper protection. Helmet and wrist guards as minimum.
Maybe also something for your shins, knees and elbows. Find some nice tutorials like UniQuest - Tutorial Series For Beginners and then just practice, practice…
Oh and start with a 20" or 24" and make sure the seatpost is long enough so you get a similar (or slightly lower) extension of your legs as on a regular bike.
If you need better advice filming yourself and posting here will make it easier to give you advice.