A little more clarification…
From Wikipedia:
XCF, short for eXperimental Computing Facility, is the native image format of the GIMP image-editing program. It saves all of the data the program handles related to the image, including among others each layer, the current selection, channels, transparency, paths and guides.
It is roughly equivalent to Photoshop’s .psd file. GIMP is basically the only software that can open .xcf files, so it’s not a good file format to use when sharing files with others. For sharing your pictures, you have to use a file format that anyone can open. The most common is JPEG (or JPG)
You have to “export” from GIMP to .jpg to get a file that you can send to anyone. When it brings up the dialog asking what quality to save as, you can often select a value of around 90 if you just plan on saving for the web, i.e. for Lenspiration. If you plan on saving it for long-term storage, you should save it in the highest quality possible. (100)