scmJS docs

Create Unit

Creates the number of units of the type for the player, at the middle of the location. A unit that does not fit there is placed at the nearest spot it fits.

Action 44 · Create Unit(Player, Unit, Count, Location);

Argument Takes Stored in the action
Player a player or group bytes 16–19
Unit a unit type, or one of the unit classes bytes 24–25
Count a number of units, 1 to 255, or All (stored as 0) byte 27
Location a location (Anywhere is location 64) bytes 0–3
Create Unit("Player 8", "Zerg Zergling", 6, "Spawn");