How does Minecraft (pocket edition) work?

I just started playing, but how do I collect wood without a weapon? Somehow it did not work with my hands. Have clicked on various trees, but nothing has happened.

Keep it on until the wood breaks, but that takes a while.

You have to hold down. I know I think what the problem is, you have no crosshairs, right? That you can in the settings, set.

Either because you're in adventure mode or you have to hold down. If you do, you'll need to go into survival mode