With photoshop, how do I make an image into a particular shape?

I'm trying to put a photo inside of a cross, to where the face of the cross is covered with the image, and the image doesn't lap over the sides of the cross. I don't even know how to search for a tutorial on this. Any suggestions?With photoshop, how do I make an image into a particular shape?
You can do it a couple of ways.





Create a layer above the image in the shape of a cross (use the selection tool to delete the bars from a solid background).





Or, if you have ilustrator, make a cross shaped path and use it as a clipping mask.