I don't understand how to join a group once the game starts

OK I get you use the Find the group page.. But once you find a group how do you join it? I know how to log on as a GM but not as a player.. I could find nothing in the tutorial about how to log in as a player. How is it done?

You have to be invited to the campaign by the GM.

Specifically, the GM will send you a link that gives you access to the game in question.  You open the link and it will take you to the game.  From there the GM should provide whatever info and sheets and so forth to play the game.  Sometimes the link will change, but unless the GM removes you from the game, you shouldn't have to have a new link every time you want to join that game.

How does a GM get a link to get people to join the game? I'm thinking of doing a game myself but I dont understand this.. How does the GM know what the link is for their game?

Create a game Ken and click 'join', once in the game there will be a link in a box in the chat (you'll have to hover over it to see the link). That is the link you can give out to players but don't post it publicly or anyone can join. The link will remain valid until you kick someone from the game at which point it will update to a new link.

A game's Creator or GM can also press the Invite Players button to acquire the join link.

The game creator can also enable the looking for players listing which when people post to it, they can be invited through it