The process in a nut shell is to draw up your design in a graphics program, cut it out by using a laser cutter, glue the pieces together and attach a saw tooth hanger on the back. Then you have a custom made awesome gift to give out. I'm going to walk through the process that I followed for the Mario collage that I made as a late Christmas gift for a friend. In addition you can also paint the individual pieces, stain them, frame the whole piece or hang it as is.
If you like any of these designs I have the finished projects for sale on my Etsy right now. If there is enough interest in a design I'll post the files that I used to cut them up there too or send it out. Message me if you have any questions about it!
Now on to the step by step guide to create the Mario Collage:
Step 1: Draw up design in Inkscape/AutoCad/Illustrator/etc.
Ponoko has some great getting started guides found here for a variety of programs. You will usually need a .svg, a .eps, or a .dxf file for most laser cutters. If your planning on submitting your design to get cut at ponoko just follow their design rules. If your planning on getting your design cut at a local tech shop or hacker space just ask them what file type they need and which line colors correspond to etching/cutting.
The process that I follow is pretty simple in that you first find an image that you want to use in your collage. Import that image into your chosen graphics program. Trace out that outline of what you want to cut out and then trace out what features you want to etch. Do this for each image you want to add to your design and then scale the design to however big you want it and move on to step two!