Scratch

There are 3 different types of galleries, some everyone can add to, some only the creator can add to, and some only the creator and his or her friends can add to. If the gallery is one that everyone can add to, or you are one of the friends that can add to it, all you have to do is press the button that says "add my projects." Otherwise, you'll have to make a comment on the gallery if you want your projects to be considered.