I’m not a Photoshop user but the other day I needed to use it in order to modify a .psd file. Usually I use fireworks.
Well in fireworks, importing an image into an existing canvas is pretty straightforward, you can even call it intuitive. However, photoshop is a little different, I don’t know much about it but I don’t think you are actually working on a canvas, but instead an image (hence the name photoshop, probably).
So to achive the import feature do the following (On Windows):
Go to File > Place
The file browser will appear. Choose the image you wish to import and click open.
You can resize at this point if you wish by placing your cursor at one of the ends, clicking and resizing. Holding the shift key allows for controlled resizing btw.
Now to finish placing it in your document, click on the move tool, the cursor looking item on your palette. A prompt will appear confirming the placement of the image in your document. Click on place.
That’s it. You can now make that collage you’ve been meaning to create.