How to crop or cut images with The Gimp:
So, let's just say that you're going to be selling women's dresses which will have pictures of models wearing them. So you want to have your images half as wide as they are high (300w x 600h or 350w x 700h, etc.). You've made your thumbnail settings to the same proportions (60w x 120h or similar). But the original full-sized image that you have looks something like this:
Obviously if you upload this as it is, the automatic thumbnail that gets created will look squashed. So you will want to cut off some of the empty white space to make it closer to your requirements (half as wide as it is high).
1. Right click on whatever image you're working on and open it with gimp. Then click on the crop tool which looks like a knife:
2. Then drag a box across the picture (doesn't matter what size).
3. A new box should have opened up like this:
4. The first two settings control the position of the box, and the second two control the size. The last one you don't need to worry about. So use the arrows to get the size and position of the area you will cut out right and then press Crop.
If you make a mistake, just click on the edit menu and click on undo. Close and save and it should be done.
After you've cropped the image to the correct proportions, you might still want to shrink it in size. For how to do that, please read the next question.