ben_collinsthose pics are photos I thought were sick and what I want to do
I'd say start with something like that train one. I don't know how the tool used is called in english but it should be something like puppet deformation, puppet warp or puppet transformation (I'm giving possible translations from how the french software is calling it so might not be exactly this).
For the one with the tree I'm not sure if the person is a picture or a really awesome drawing but for the roots and the grass it seems like they mainly used brushes. The ribbons too look like they could be brushes (where they played with the opacity a bit). Just put your main elements in position on different layers and think "how can I make them all look like they're part of only one creation?" Then play wih the layers' order and blending modes, add brushes you think might be useful, follow tutorials on more elaborated techniques you might need, etc.