I want to make a Tower Defense game using the StarCraft 2 editor.
How can I make a rally point to control AI appear at one point and go to specific point? How do I make creep spawn properly at specific times?
You need both Locations and periodic events for the functionality you've described. Using locations, you can create a trigger to order all enemy units in location A to move to location B.
Likewise, you can make another trigger to generate enemies in location A every x seconds (which can then be ordered by the first trigger to move towards the goal area).