Annette, the smoker is a must when dealing with swarms. How will you get the remaining bees in the box?
Answer, 2 choices. 1) wait til dark, possibly not an option if you live more than 10 miles from the swarm.
2) This is how I do it Annette. Shake the bees in the box, and let them orient to the box. Pick up the box just off the ground and hit it gently but swiftly against either the ground or your leg. The bees, most of them will drop into the bottom of the box.
Get the lid on, quickly.
Allow bees to orient to the box some more. Most will enter through the one opening you have allowed either by cutting a flap or bottom entrance, use a reducer, of a hive body or nuc.
When most are in the set up, smoke the ones on the outside lightly, directing them into the entrance.
Not all of them will go in, but seal the box anyway. Goes without saying, but worth mentioning make sure your box has ventilation.
If you have to leave and all but a dozen or 20 or so bees are left behind, you could tell the people or you could do it, set up a small box under the tree or whatever with a small piece of comb or a little lemon grass.
The stragglers left behind will either go in the box, cluster on the tree or fly away and even possibly join up with another hive.
If you want to get every last bee, then leave the box there and go back at dark.
Catching swarms is about timing, you must go as soon as you get the call, or the swarm may leave.
Most swarms will stay in cluster anywhere from 1-3 days with 1 day being the norm, although I've caught many that were there 2 or more days.
Have fun, good luck and if you have any more questions please feel free to ask.