Lol

We all have to start somewhere.
Well, I'll just teach you how to walk on water... Then, you'll basically automatically learn how to walk on tree trunks, because walking on water is just a more complicated version of walking on tree trunks.
Focus chakra in the soles of your feet. Keep a constant flow going. The specific amount of chakra that you'll need to stay standing will vary while you're standing on the water. Too much chakra, and you break the water's surface tension and fall through. Too little chakra, and you can't support your weight and you fall through. You're going to have to constantly modulate the amount of chakra necessary to stay standing while on the water, just through trial and error. Eventually, you'll get the hang of it to the point where you do it without even thinking about it.