Ok so to start off a one hander is mainly a commitment trick and no its not riding down the street and taking your hand off. Its done in the air you dingbats.
So to do a one hander you will need to know how to bunnyhop so you can get higher on a ramp.
So the best things to learn these on are on any kind of tabletops or flyout jumps or even kickers.
So what you want to do is approach the ramp with a decent speed. Then you want to jump the ramp.
When your at the peak of the jump which is in between taking off and landing you want to take your hand off of the bars. You will most likely leave your dominant hand on for this trick so if your right handed take your left off vice versa. So when you take your hand off you dont want to just throw it way out you want to start off little by little.
So start by barely lifting your palm up off the grip. Then once you get comforatable start raising it higher. Once you start getting it about a foot off you want to start throwing your hand out to the side. Remember practice practice practice.
This trick should mainly be done little by little on a tabletop or ramp until your ready for the bunnyhops.