What can you do at cuba?

If you mean what can you do when vacationing, it really depends on the area since some have beaches while others don't. Apart from that, you can always go to a hotel and spend a nice time there and go to the pool. If you are staying at someone's house, you can always walk around and get to know different places. In Havana you can go to the aquarium, circus, zoo..., in Varadero you can obviously go to the beach and the wonderful places they have there. It really depends where, so you should specify. Other than that, you can make new friends (Cuban friends are extemely funny and compassionate) and have some fun! Or you can go to cabarets, clubs, shopping centers....
Hope I helped! Good luck