Tokens are the currency of Conversifi. You spend one token each time you have a learning session, and earn one token for each coaching session. You can check your token balance in the upper-right hand corner of the screen. If you have questions about your balance, the best place to start is the the Ledger tab in the Payments link, which shows all the tokens you've earned, bought and spent.
You will need at least one token to begin a lesson as a learner, so if the option to practice your target language is greyed out on your screen, you'll need to coach or buy tokens before your session.
Click here if you need to know how to buy tokens.