Ok, so I’ve never used it so this is just the general gist of how it should work. You should be able to create layers in the document. Ideally you want to make the page size (possibly called an artboard) a rectangle big enough to fit the guitar image/shape at life size+ a couple of mm. If your machine struggles making the image life size you can work at 50% pretty safely and let the printer scale it up. Paste and scale the guitar into a layer and then lock it. Then you need to make new layers for each of your bits of comic art. Paste them in and start arranging. You should be able to drag the layers above and below each other to make the art work overlap how you want. If you are still struggling, pm me the photo of the guitar body and some measurements and I’ll set that up for you to work from as a single jpg layer.