playMGM uses the concept of tournament dollars (T$). If you win multiple entries to tournaments, any extra entries will be exchanged for tournament dollars which you can use to buy-in to any real-money scheduled or Sit & Go tournaments (except Heads-up STT).
You can check your tournament dollar balance any time by going to the "My poker" page under the "Account" section.
If you don't have enough tournament dollars in your account to enter your chosen tournament, the buy-in window of the tournament will display a combination of your tournament dollars and regular dollars. You can also elect whether to deplete tournament dollars first or regular dollars first when buying into a tournament - this can be set in the "Preferences" section in the client.