type into the text buffer the dot command,
.join GAMEID
So, if you wanted to be a gunner for me, you just have to FIRST ask. Then if I say yes, you type:
.join Kermit
Then I have to accept you by either clicking the accept button or typing:
.accept emalo.
You can review all the dot commands in the help section.
Once you are joined with me, you can go to the gunner positions with the number keys above your letter keys.