When honey bees swarm they are docile as they are not protecting their hive. In fact, they have left their hive with their old queen and are looking for a new home.
When swarming, the bees find a perch and surround the queen. They send out scouts who visit all the possibilities in the neighborhood, then come back and give the details to the group who come to a consensus.
You can capture a swarm of bees by simply brushing them into a box, or (if you have a ladder tall enough) cutting the branch and letting them gently drop into your box. You then carry them home and shake them into the empty bee hive, and hope that they approve!
If you do not have a ladder this tall, you should call Marvin Johnson, our favorite BeeGuy.