"Tu cumperi azi o tablă neagră."

Translation: You buy a blackboard today.

[gplano]

The word order 'today you buy a blackboard' should be accepted.

[LABv7L1N]

Is this an order telling someone 'You buy a blackboard today!'. Otherwise it isn't good English. Maybe 'You are buying a blackboard today' would be better.

[LouisSepdekdu]

The imperative would be cumpără.