What do you do with a cluster of bees?

By cluster, I suspect you mean a swarm on a tree or post or something similar.
The answer is, other than telling a local beekeeper about them there is nothing you really can do. After a period of time ranging from a couple of hours to a couple of days they will move on.
A beekeeper would check the swarm and, if they are honey bees, would probably collect them and put them in a hive -- after all, the swarm is looking for a new home.