Can Enterprise join a Common Market?

Hello, can Enterprise join a Common Market? if can, where the button or page for my Enterprise join Common Market?
Recently i get some invitation join Common Market but due im didnt know where i can click Join...

Yes an Enterprise can join a common market. In your messages there should be a message from the common market that would like you to join them. End of message should say Please join us! Click on that and then join. Hope that helps.