It depends on which program you use to save/edit your images.

With Gimp, all you need to do is go to Export and then specify .webp as the file extension. However, most programs offer a selection under “Save as” or “Export” – and not all programs support webp.

I briefly looked at your latest posts, where the images are uploaded as .jpg files. That's good, because it's also a compressed format. I think you can save yourself the effort of converting .jpg to .webp.