i need to know how to make units burow with a triger... i need it for me and the zeklings defence map
There is no way to make them burrow with a trigger. You can create a burrowed unit and remove the unit. You can run an AI scipt and make sure they have burrow enabled and they will all burrow.
If you have burrow enabled and the computer isn't doing anything, it will automatically burrow. Usually.