You can upload images, but you can past a link to a Google Drive or Dropbox. But for sharing you work images are usually fine. Did you start for the very first time with CATCH? If you’re totally new to Blender, I would recommend starting with the Blender Basics and Fundamentals. Linking you up:
https://cgcookie.com/courses/blender-basics-an-introduction-to-blender-4-x
https://cgcookie.com/courses/fundamentals-of-3d-mesh-modeling-in-blender
