Just google for things that confuse you. Your needle is made from simple steps. Just make sure you draw the needle on a separate layer, so that when you export it you can do it on a transparent background.
Open GIMP and a new image. Make the image square and of sufficient resolution. Since you will be rotating the image, there will be some quality loss (minimal, as the rotations will not be sequential). Make sure you choose a resolution 2x or 3x your final resolution so that you can shrink the images to the target resolution and not loose much quality.
Always draw in layers. This makes changes much easier (I cannot stress this enough). Immediately make a new layer (right side menu), call it dial. This will be your template for your needle. Draw your dial on this. You can also make a new layer for all the digits if you want. Then make another layer and call it needle. This will be your important layer.
I draw using the beizer tool (B on keyboard, it is called the paths tool in GIMP). You click and drag for curves or click points o the image to make a shape. Hold ⌘ and click on the first point to close the shape so that you can fill it with a colour/paint. Now click Selection from Path on the left side menu. This creates a mask based on what you just drew, so when you fill with a colour, it will just be inside.
Choose the bucket tool (shift B) to fill in the colour. The default colour is black so change it if needed by clicking on the black box covering the white box. Then fill in the needle.
When everything looks ok, hide the non-needle layers (the eye icon) and export to png. This will give you your needle, like in the zip in my last post. Now use the script. You might have to tweak it a bit to fit your project.
If any of this doesn't make sense, just look for guides to the specific steps, like how to make layers (ex. search: gimp how to add layers).
Hope this helps.
