There are pluses and minuses involved with both options, and you should weigh each matter carefully before making a final decision.  Basic photo editing software is often sufficient if you only plan on creating simple collages, but it may not provide the right sort of tools needed to create more complex designs. If you use photo editing software you already have, you save on expense. Some special photo collage software is free, but the highest quality options do cost money and can be fairly expensive. Creating a photo collage with basic photo editing software can be labor intensive and time consuming. Special photo collage software often comes with templates and tools that make collage creation easier. Every program you might consider using has different tools, so you will need to look up a specific guide for your software in order to learn how to use it effectively.  Begin by searching through the software help files or the software's instruction manual. If you find nothing within the help files, search the Internet. Tutorials can come in all-text form, pictorial form, or as video tutorials. Browse through a variety until you find one that seems helpful. Many programs allow you to undo your changes if you decide later that you do not like them, but just in case, it helps to save your collage each time you feel satisfied with your progress. That way, you can return to an earlier version if you later decide that you do not like the most recent changes you made to your collage. Saving frequently also helps to prevent you from losing your work. The quality of a digital collage can be dramatically affected by the quality of the paper you print it on. Standard printer paper is light and has a poor effect. You should at least consider using cardstock or photo paper. On the same note, you should also use a high-quality printer to ensure vivid coloring and depth.

Summary:
Choose between your current photo-editing software and photo collage software. Read tutorials for your software. Save multiple versions of your collage at different stages. Print the final collage on high-quality paper.