Here we have the picture of a girl with devil wings. Now I’m only interested in a girl for my project so we have to get rid of background. I will use Quick mask and simple rough edged brush to make a selection of this girl.

Select Brush Tool.

… And begin to cover the area with mask. Try to stay close to the edges.

Refine the edges if needed. You have the X key to switch between Cover with mask and erase the mask.

Tap Q again to switch to selection mode.

Now we will create a new document

with the same dimensions as our initial image.

And here are the dimensions.

Select inverse before you drag the girl to our new document.

And here we have the girl on a new document. We will work with this document now so you can close the initial image now.

I will also rotate my girl a little bit at the very start.

Now I will refine the edges of the girl, especially the hair and the wings, when there are a lot of tiny details there.

As we have our image on a new layer we can use simple eraser without spoiling the background.

And here is our result.