To move or resize everything in a layer, click the layer you want and press ctrl + t.
If you only want a piece of a layer, use the lasso tool first. When you lasso what you want to select, it will show the bounding box where you selected with your mouse/pen instead of just the pixels. To fix this just move the selection anywhere to refresh it and then undo. It will then show the selection on only the pixels present in the layer.
If you want to select things on two different layers, just click both layers while holding down shift and then press ctrl + t or use the lasso tool.
(I know this forum was made two years ago but it still popped up when I was trying to remember how to do this and it took me a while to figure it out)