MARS is subdived into seasons, the seasons are the period that is established to play the corresponding turns. For example, if a season has two turns you can play them in the time frame established for the season to last.
A turn is considered a complete game cycle in which you create and answer questions, earn GCoins, construct and evolve buildings. Once you perform all these actions you go to the next turn and perform these actions again.
When you enter in the map of the game after viewing the results of your previous turn, you have to enter in the R+D center to create and answer questions. Past this action, you can use the GCoins that you earned to construct and evolve buildings. Once you are satisfied, you can go to the following turn by click on the "Next Turn" button located at the bottom of your screen.