In order to join a station you will have to accept the invitation sent to you via email or message on your profile (if you have already signed up to Radiojar).
Once the owner or administrator of the station invites you, you will receive an invitation like this one:
Click on the link and you will be directed to this page to signup:
Complete the procedure to signup and click on the Signup and accept invitation button.
If you have been invited to host/co-host a show you will view this when signing in:
Clicking on the show will take you to the management section of your show where you can schedule it (provided that you have the access), manage the content you want to broadcast, add other hosts and edit all the details of your show.