There's various ways you can do it if you have any kind of photo editing program. I used an online though. It's called:
www.picmonkey.com
Once there, go to "Collage". You can tinker around with different layouts, and just upload your saved pictures onto there. I think the standard default collage has room for 3 pictures. If you mess around though, you can find room for more... or less. And after you're done with everything, just save, and choose the destination on your computer you want it sent to.