The cool thing about collage is that anybody can do it! All you need are a few tools, papers, stamps, backing, and medium (e.g. all-pupose sticking sealant stuff) - all items you can find at a craft, art, or maybe fabric store.
To make the collages I posted Monday, I started with a stack of masonite squares cut to 4x4". You could also use illustration board, canvas, wood - anything that will hold up and be acid-free.
I coated the masonite with gesso (primer), let it dry, then painted the edges with plum acrylic paint (I use Golden, but any craft paint is fine).
Then I cut a paper background to 3 7/8" square and coated the masonite and the back of the paper with acrylic matte medium (I use Golden, but you can use Mod Podge, Liquitex, or whatever - matte or glossy, whichever you prefer). This bird paper is my favorite and I wish I could remember where I found it! Art paper is good, but so are cool wrapping papers, book pages, magazine pictures, etc. Thin papers must be treated with care, but they will be durable by the time you are finished.
I then tore a strip of another paper and/or cut paper shapes and glued them on with the medium. If you're going to use stamps, use them now before you put the medium on the printed side of the paper - otherwise your stamp ink won't sink in and will get messed up when you paint on the medium.
Then add flourishes: words out out of a magazine or book, shapes punched out with a paper puncher, engraved illustrations, postage stamps...the possibilities are endless.
Finish with a coat of medium - I finished with glossy and put it on thickly so that it would have an interesting brush texture. Let dry, and you will have a fun piece of art you made yourself!