This may be a redundant post, but someone recently asked about making collages so I'm doing a quick tutorial with my limited expertise.
I use Picasa for viewing and editing my photos, it's free and easy to download. I store my photos on my computer, not on Picasa Web Albums.
To begin, open Picasa and choose your photos.
The green push pin icon in the bottom toolbar holds the photo, allowing you to select a number of photos. The red circle will take away any you don't want.
Click on "collage," found in the bottom toolbar.
The left window allows you to choose whether you want a picture pile (as above) or a mosaic, grid, etc.
In this picture pile, each picture can be rearranged. Right clicking on the photo gives a number of options.
To set one photo as background, click "set as background."
To change the border, click "change border," then "white."
Each photo can be manipulated as to size by clicking on the photo and scrolling up or down. When you click on the photo a circle will appear. The little orange button to the right of the circle enables you to change the angle of the photo.
When you're happy with your work, click "create collage" and voilà, you have a beautiful work of art!
Since my house is not yet decorated for Christmas (it's hard to decorate a dusty construction zone), these are photos pulled from 2008.