well for monster spawns, its handy to make a unit-type variable with an array, and go fill in those variable arrays with unit types at the start of the game (melee initiaziation as event) so you can later on use those unit-types to spawn.
to spawn the units, you need to take the action "create unit" choose the variable array to pick the unit type, then fill in an amount and a place (like a region or a map cooirdinate).
you could possibly make the event for the unit creation, periodic, but this is basicly how you create spawns.
