Newbie tries to join circle sections to make mesh... ???

Hi ~
I’m trying to make a mesh shaped like a sliver of a crescent moon that I can extrude later. I’ve created two circles and trimmed them into two different size arcs (with the knife tool) and I wish to simply join the ends of the two arcs together to make a solid crescent moon shape.

In edit mode I cannot select the end vertices of both arcs to join them.

What is the best approach to making a crescent moon shape, please? Looks like it’s not the way I’m doing it, right?

Thanks for any help!

In edit mode I cannot select the end vertices of both arcs to join them.
Join together selected objects with Ctrl+J. You can then edit them asa single object

Thank you, Richard.