You are correct Malachite, but Jen may need it explaining further. Jenny... you will firstly need to transfer that image over from gumtree(or any other site that hosts images) and file or save it to your device.(whether laptop, desktop, or tablet)
Now as Mal says right click on the image, and choose save image(or picture). You will be given options,. Perhaps pictures is the least complicated if it is there. You will see a box, probably highlighted in blue that says "save as". You can rename it there and then click "save" in the smaller box below.
Now if you want to print it or send it, all you need to do is go into your picture files and right click on the image. Then choose OPEN and either choose the print option using the icon top right or, ctrl p.