The lobby shows the list of available matches. It appears when Flexwords starts and whenever you leave the other screens. You can refresh the list by pulling it down and letting go.
The matches are placed in three categories: Your turn, Their turn, and Completed. You can delete a completed match by tapping its button.
To continue playing a match, simply tap its panel. If the match isn't finished and it's your turn, the button will be enabled.
Matches that appear in yellow are invitations from other players. Opening such a match will give you the option of accepting or declining the invitation, and if you accept, you can play your first turn.
Matches that appear in orange have data errors. You can delete them, or refresh the match list to see if the match(es) load properly. An erroneous match usually can't be opened.