Advice for a certain type of mission

[Praetorian]

Hey there, I'm not quite sevy with mission editing quite yet, so "scripts" and "triggers" aren't something I quite understand (yet).

So I was hoping someone could help me out with a simple mission I'm making.

I'd like to have it where I have a simple base with all my men holding it whilst waves of numerous attackers keep.. well... attacking..

The question is, how do I make it where the enemy continues spawning at certain locations and just keep attacking? Heck, doesn't even have to be a huge variation in unit types, I just want waves of attackers to fend off till death.

I'm guessing this heavily involves triggers/scripts, so for whoever who takes the time (I'm very grateful for by the way) to explain this concept to me, explain it as if to a... retarded rabbit perhaps? 

In a sense, for those Gears O' War fans out there, take it as a question of how to do a fairly easy horde mode in ArmA

Thanks!

EDIT: And per say I wanted a small stream of reinforcements to come in as well? Thanks again