How to edit a selection

[grinolot]

I know there are multiple steps involved but how can I accomplish the following - move and re-size, make the edges softer so it blends in better, place the image behind the trees?

[JoeB]

I know there are multiple steps involved but how can I accomplish the following - move and re-size, make the edges softer so it blends in better, place the image behind the trees?

Which image, the one with the grey background or the one with the colored background on the right?

In either case the image you're working on has to be on its own layer. Then use either point-to-point or freehand selection tool with anti-alias checked and some feathering (the amount will depend on the size of the image) and perhaps a little Smoothing to outline the girl, invert the selection and hit Delete to delete the background from her. Then just copy her layer and place it on the background you wish to put her on, move her layer into position with the Pick tool and also use it to resize to fit. If you want to put her behind trees then you'll have to have her layer below the layer that contains the trees and remove anything from that layer where you want her to be showing through.