There's a slim green/yellow/red light to the left of your name.
This is your ping. Green = good, Red = Bad
To the right of your name there is a Green/red box.
When you're ready you click the box (currently red), turning it green, showing the other players you're ready to start.
If you want to change something, like your team or civ, you click the boc again, turning it back to red, you can then change things.
When all players have checked their ready boxes to green (or "clicked in") the game automatically starts.
Green = ready, Red = Not ready.
Don't judge those who try and fail.
Judge only those who fail to try.