Grey circles? Whats that?

Have you finished the lessons that aren't greyed out? Typically finishing the available lessons will open a new set.

If you're talking about the skills on your tree, the grey color indicates that they are not available yet because you have to finish other -generally less advanced- skills first. Finish the last colored skills in your tree and the grey circles on the next row will become available.

you haven't unlocked it yet thats why