Trials Riding Backhopan absolute basic move
The backhop is the most basic move to start understanding most techniques in trials riding. Once you have that, it is quite easy to extend your skills to a few hops on the back wheel, before you can hop your way on the back wheel in any direction... It is also a similar move that you'll need when launching a bunny hop or to climb sideways...So it's really hardcore basics.

Three phases smoothed in one move
1° Start from a stand still, brakes full-on, shift your weight on the back wheel. 2° Lift the front wheel and push on the legs to jump, extending the arms before lifting the bike. 3° When the back wheel takes off, pull your knees upwards and carry on lifting the bars.
4° After that, gravity pulls you back to earth, nothing special. Try to land on the back wheel first, it's smoother. See the move in a video

Lifting the bike in a bunny hop or back hop?
Lifting the handlebars is the only trick, because your feet can't lift the bike. It looks like the feet are stuck to the pedals, but in fact they are just limiting the ascension of the bike. During the extension, the arms are kept low to keep the rear wheel pushing on the ground, but as soon as the extension is over, its time to fold back the knees with a synchronised pull on the arms upwards to lift the whole bike. All the move takes less than a second.
Another blurred video.
A pedal kick to boost things up
If you can't take off
There is a mix of reasons...Sometime, the problem may be that your effort to jump is in conflict with your effort to pull on the bike (like trying to lift a stone while standing on it). It's a synchro problem. You can add a pedal kick to it, during the extension and while pulling on the bars. If you are in good shape, and pull all your strength doing the right move, it's like doing gymnastic, you can jump high. Then with the right move alone, and vague effort, you can still do a back hop a foot high, which you could manage with plenty of muscle and very bad technique too...
Basically the better the technique, the less effort...It is really true, especially when bouncing on the back wheel. The next step is to Bunny Hop over something. For the bunny hop, exactly the same move except that you don't use the brakes. Do it at any speed you like.
Or try out some pedal kicks to move forward.