Do you mean pasting an image inside a square? If so,
1) Position your image file over the square.
2) Cut the image: command-x (Mac) , or control-x (Windows)
3) Select square.
4) Paste inside: command-shift-v (Mac), or control -shift-v (Windows)
To take image out of square, or cut contents: 1) select square 2)
command-shift-x (Mac), or control-shift-x (Windows)
If this wasn't what you wanted and you already knew this you've just made me
look foolish.:) In that case, you'd have to be more specific or provide more
Hope this helps.