To start out, you're probably wondering what the heck G.I.M.P is. GIMP is a GNU Image Manipulation Program; which in easier terms is like Photoshop. GIMP is free, so it's a great fix over paying for Photoshop, who's cost is outrageous. You can download it here. GIMP works for Windows XP Service Pack 2 and later, and also comes in many different languages.
Step 1. Well, you've installed GIMP and you're wondering where to start. Click on the 'File->New' tabs and set up a new image with the following dimensions: Height- 150px and Width- 600px. These are the maximum dimensions allowed for TPG forums. Something I recommend: instantly save at the start so you can save quickly and you can always come back to it when you need too.
Step 2. You have your blank white image, and it's time you find some images to place in the sig. My favorite site to use is Planet Renders. You do need an account, but it is well worth the annoying registration. I decided to just search "Sniper", and after going through a couple of pages of cut-outs of snipers from different games I decided to use this one: Sniper. I copy and pasted the image into GIMP and scaled it with the scale tool (Shift+ T) and moved it into a good position. Now you might be thinking, "well its just a black background and I don't want that!" Solution: using the Fuzzy Select Tool you can select parts of the image and by using the background eraser, you can take away parts of the image. A reason I chose the image is because, 1) It looks nice. 2) I was able to cut out the background very easy. Some images you have make a path around the part you want cut out, which takes time and effort.
Step 3. You have your image in and now it's time to put in your own background. I decided to search in Google images "Gun backgrounds". And came up with this: Background . You copy and paste it in the image and adjust the layers so it's behind the sniper image... but it doesn't show up! Solution: 1) Select the sniper using the Fuzzy select Tool. 2) Left click on the sniper layer and select "Add Alpha Layer". What this does is to let you use the background eraser tool to make things transparent. So go through it, selecting each part of the layer and remove the background of the image, soon your new gun background should show up.
Step 4. You have your sniper and your gun background, and the only thing missing is, well, your name! So click the Text Tool, and create a text box in the image. Add in your text and move the box where you need it. To adjust the color, font, and size, go to 'Window->Dockable Dialogs-> Tool Options.' That should bring up the menu to adjust everything. Also a great site for free fonts is dafont.com. After that, you can adjust opacity and other things that get complicated, but overall you have just completed your first signature!
Conclusion: Before you start using GIMP, there's a few things you have to understand. GIMP is free, but compared to Photoshop in user friendlessness and options, Photoshop sweeps the competition. So the messsage here is, if you're looking into some serious editing, I would highly recommend buying a version of Photoshop. I personally own Photoshop CS5 and absolutely love it.