When you are only able to select the coaching option, and you cannot complete a lesson as a learner, there could be two potential hiccups.
1) Ensure that you have enough tokens to complete a conversation. Tokens can be purchased or they can be earned by coaching students in your native language. You can check your balance in the top left of the screen, in the small "$" icon. The balance must be 1 or greater to do a learning session.
2) Check to see if you've selected a target language under Profile. Go to Profile > Language I'm Learning. This will allow you to search for a corresponding coach on our main page. Don't forget to click on Save changes before leaving this screen.