The collages are super, super easy to make. I use a program called Picasa, which is a fantastic free photo organization and editing program (for either Mac or Windows) by Google.
I'm going to assume in this tutorial that you have downloaded and installed Picasa, have loaded your photos into it, and are fairly comfortable clicking around on stuff.
For my example, I'll use some photos I took at a UAH hockey game in February. I've got nine here to play with, but to start off I'm just going to take four of them. You can select photos by clicking on their thumbnails. To select multiple photos, hold down on the Command (Control on Windows) key while you click each image.
Once you've selected all your photos (you can release the Command/Control key now), locate the Collage button along the bottom of the application screen and click it.
Clicking the collage button will bring you to a screen that looks something like this.
If your screen doesn't look exactly like mine (you have a different aspect ratio selected) don't worry. Look at the controls on the left hand side of the screen and locate "Page Format." Click the down arrow next to the box to display all your options. Here I've selected a 4x6 format.
An interesting tidbit about this setup- if you choose four photos and the 4x6 format and have your layout option (the control for that is at the top of the left-hand side of the screen) set to Grid, you'll get four wallet-sized ready to print on a single 4x6 sheet. Such an easy way to get wallets (2x3) with just a few button clicks!
But what if you don't like the way that Picasa has cropped a certain photo, or you want to do some editing on that photo before printing? That's really easy, too. You can choose just one photo in a collage and then click the "View and Edit" button right below the collage display area. That will take you to an editor where you can adjust your crop, change white balance, etc, and when you're finished you'll be taken right back to the collage menu with your new edits in place.
Now that I've shown you the wonders of easy wallet-size formatting, let's try something a little different. For this example I've selected six photos, and I'm going to change the photo layout to Mosaic.
That gives us a really nice collage with different sizes of photos. I also changed the Page Format to 8x10, which is a really great way to easily fit lots of photos into a single 8x10 print. You get an awesome looking collage without having to resize and move everything around in Photoshop- just a few clicks and Picasa does it for you.
If you want some white space between and around your photos, Picasa has a control for that, too. Locate the "Grid Spacing" control on the left-hand side of the screen and simply drag the slider to the right until you're happy with the spacing. At this point you could also change the background color to something other than white or even add drop shadows.
Adding some Grid Spacing gives a nice bit of separation between photos so they don't all run together.
If you don't like the order or arrangement of the photos in the collage, you can change that, too. Just click on the "Shuffle Pictures" button below the collage preview. The effects of this button can be pretty random- you don't really get any control over the sizing and placement of your photos in a Mosaic layout, so you may have to click it several (dozen) times to get an arrangement that you like.
But it's really pretty good for moving your photos around. I find that I eventually settle on an arrangement that I'm happy with.
When you've finished tinkering with layout, page size, grid spacing, and any other options, you can create a JPEG file of your collage by clicking the "Create Collage" button. This will create a new file in the Collages album in Picasa (and also on your hard drive). It should be all sized and ready for you to print or upload.
And, for those who were wondering how I do my monthly wrap-up collages, there's only one trick to it. You have to have a square number of photos (as in 4, 9, 16, 25, 36, etc). If you don't have a square number it will still work, your individual images in the collage just won't be square.
As an example, for most Friday Favorites posts I have 9 items to share. I choose those 9 photos to create a collage with. I set the layout to Grid, the Page Format to Square (CD Cover), and the add some Grid Spacing. Monthly wrap-ups usually have 25 or 36 photos, but they use the same settings- grid, square, and grid spacing.
And that's all there is to the basics of creating a collage in Picasa. Note that my post only scratched the surface of the options available. There are other layouts to choose from besides Grid and Mosaic, and if you have your individual photos cropped to sizes other than a 4x6, you can help the Mosaic layout determine the best sizes for your photos, giving you even more options.
Have fun creating Collages!