I recommend Photoshop if you have it. If you don't, Paint also works, but my
prefenace is photoshop. any alternative is to take your photos to your
local walmart and make copies, or if you have film reprint them. Then
actually cut out the pictures and set in a paper format and then scan the
finished piece into your computer. thats the long way around, but still
works.
There isnt any "collage" option in photoshop or paint. The way I do it is I
use the "wand" tool to "trace" each photo I want then copy and paste it onto
a new document. Repeat with the next image and place to where I want and find
a nice background to put them all on, or make my own.
There are some scrapbook softwares out there that may make it easier for
you, I'm not sure how easier since I have never used them myself. But I know
they are out there.