Hello! I'm giving a very short tutorial on how to make an icon square (since I often saw many un-square icons). You don't need Photoshop or GIMP or heavy picture editors. Here I'm using link
1. Click "Editor". Here you'll see a Photoshop-like layout.
2. Click "Open image from computer". Select your icon or any picture you want to make square.
3. Click on the "Crop" icon on the top left of the panel. Choose "output size" on the "Constraint" dropdown. Enter 200 x 200 or whatever square size you want.
4. Drag the mouse over your picture. Hit Enter.
5. Don't forget to save your square picture!