[x42bn6]

Open up the Trigger Editor and look around. You can create triggers, which consist of Events (that "activate" the trigger. Triggers do not need to have events as they can be manually invoked but for this case, it is most likely an Event is needed); Conditions (conditions that must be satisfied before the Actions occur) and Actions, which do the actual work.

You would create a new trigger and rename it something sensible. Then think about how the creeps will spawn. Is it going to involve a countdown? If so, there are triggers for countdown timers. Does a player type in something? There are chat triggers. Choose the appropriate Event that you want and fill in the red links.

The same goes for conditions, depending on how you wish to restrict it.

As for the action, you choose Unit - Create Unit (may have lots of similar triggers - I can't remember) and fill in the red spaces.

The Wait [0.01] seconds is a due to the fact the computer cannot spawn units in an infinitely small amount of time, and some units might be in the stage of processing when asked to move, so some units get left behind.

Unfortunately, you cannot order all units to move in a region. But you can Pick every Unit in Unit Group and Order them to do something, and there is a trigger for that.

The hardest part is the red links to fill in.

Have a little spin with the World Editor. If it doesn't work, then get back to us with your triggers and we will correct them. This comes with experience.*