When fishing with more than one fly you attach a point fly to the end of the leader and tie on droppers. We prefer the latter as it is easier to tie and seems more reliable. Remember that when using the Water Knot you use the lower section of line for the dropper and cut the top off.
Droppers have a habit of catching around the main leader.
One way to reduce this is to stroke the dropper out until it stands at right angles to the leader, then pop a dab of fishing glue over the knot and the very base of the dropper. Some people who can not master knots put droppers on by tying tiny metal rings to the leader and then tying the droppers to these rings. The disadvantage is that their weight tends to pull the flies quickly out of the fishing zone.