You mean when you bring a unit to a location and it starts a new wave of people? There are many ways to do it. All you need is something to count. Usually it is either using switches or using deathcounts.
I'll explain the deathcounter method
If you don't know what deathcounters are read this
http://www.staredit.net/index.php?tutorial=124Anyways, make a trigger like this
| Trigger |
| Description: |
| Setting levels |
|
| Players: |
| ¤ Current player (does not need to be current player) |
| Conditions: |
¤ Death of "Rynadon" (does not need to be this) is 0
|
| ¤ Bring "current player" atleast 1 "anyunit" to "start" |
| Actions: |
¤ Create "whatever you want to spawn"
|
¤ Set deaths "Rynadon" to "add 1"
|
| ¤ Move "whatever unit" at "start" to "back here" |
Then you basically make the same trigger and make the deaths to be atleast/exactly 1 and make it spawn different units. Next make the death be atleast/exactly 2 and so on and so forth.