It does pretty much everything that Photoshop does and is 100% free, compared to the hundreds you could pay to do the same thing.
Have you ever tried to put an image on something you have created and the image has a white box behind it and you didn't want it there? I can show you how here.
1) After downloading (and opening Gimp), click on "File" and open whatever graphic or image you would like to take the background off of. Do you see how the white square takes away from the creation? Let me show you how to make it transparent!
For demonstration sake, I made a simple bubble in Powerpoint and filled it with a water pattern, saved that image as a jpeg, and then opened it with Gimp.
2) Next, under "Layer", scroll down and click on "Transparency".
3) When "Transparency" opens, click on "Add Alpha Channel".
4) After clicking on the "Add Alpha Channel", go over to the tool box at the left of your screen that popped up automatically when you opened Gimp and select the "Fuzzy Tool" at the top right side of the box.
7) Once you hit the "clear" button, your image will look like this.
8) You can now click on the "file" button and scroll down to click on "export".
You HAVE to do this if you want to save it as a jpeg or a png file. Once you do click on the "export" button, you will have to tell it to "export" one final time.
9) Now, the background behind the original bubble is clear and I can place it back on my blue background and move it to wherever I want to. I can even adjust the size of the bubble as much as I want to!
I hope this tutorial was helpful. Do you use any free open-source software for your classroom? If you do, I would LOVE to hear from you.