How to get it?
These are small jump impulses, followed up with a lift on the bars while tucking the knees. The body weight must be quite above the stem, so that when you spring up up using the flex of your calves, you can pull up the whole bike with you by just keeping your arms firms with your upper body. Try to minimize the hops' amplitude and height, and eventually, the frequency of the hops to save your energy for the next big move.
Else, you'll get tyred very quickly and won't last long on the bike. Most of the time, you don't need to give any pedal kick, it is like doing fast push-ups during the tyre compression, synchronised with the spring effect of flexing your calves. Once your body has moved up from the extension, a good grip on the bars naturally lifts the bike (no need to pull very much). A good exercise is to balance across some stairs, with the wheels on different levels, and try to hop up the stairs, or sideways along the same level. Once you can hop, try to adjust your push-ups to the minimum effort. Nico's push-up are an overkill for these poor little steps.
Change of direction
If there is some gap between the front wheel support and the rear wheel ground, or there is no convenient space for turning around progressively with a few hops, you'll need to pull on the bars and "jump in one extension" to take off both wheels at the same time and land them directly onto the final position. In some cases, a small push on the pedals just at the end of the extension helps a bit the move forward.
Another scenario is to turn 90° or more in one energic hop, to land both wheels onto a completely different track. When turning in one hop, the bike mainly follows the shoulders. During the push up impulse, rotate your shoulders towards the direction in which you want to end. Try to face towards your final direction. That way, when lifting up the bike, you will only need to naturally realign the bike in line with your upper body. In some gnarly steep rocky tracks, your only way up is bouncing sideways or forward with constant repositioning for balance. To move forward more easily, accelerate each hop with a smooth pedal pressure when the tyres are about to take off (not when in full support).