Beginner here: what makes the board bounce when doing an ollie?

Just two days on a board... I know I don't have to start doing tricks so early, but out of curiosity after watching tons of videos on you tube, today I tried to just make the board bounce from the ground after jumping on it. Instead, I just jumped, but the board remained still. I tried many times and not even once I could make the board bounce. What's the trick?