__ is set?

Switches are either Set or Cleared.

The condition "switch01 is set" will only be fulfilled if you have a trigger with an action that says "Set switch01". They're binary variables which take up a string, and have only one advantage over death counts: randomization. If you need to know more, you need to elaborate your question more.

Can you explain it in context of a Special Forces map.
Also, what is randomization?

Randomization is simply randomly (50/50) selecting the switch to either be "Set" or "Cleared" This is always random. For 1 switch the chances are 50/50.
For 2 switches the chances are 25% (for each outcome
...

The more switches randomized, the more possible outcomes.

Also, "Set" = "Set" in the text editor and "Cleared" = "Not Set" in the text editor, just for some clarification.

ok here's how i understand it:

a trigger sets (or unsets) a unique switch with the action "Set Switch"; and a second trigger, which has to be after the former trigger in order for it to work (or not work), is "triggered" when the condition Switch, which refers to the same unique switch as the former trigger, is met.

This is some nice boolean logic. And, in the context of a Special Forces map, it prevents the game from ending in defeat at the beginning by having the "Create Special Forces Recruit (civilian)" trigger sets a switch, which the "When current player has at most 0 units, end in defeat" trigger needs to be implemented (and not until then!).

Thanks again... now for some fun!

Can you explain randomization in the context of a SF map, please? Like what conditions and/or actions are used for Randomization?

Is this for the randomization of unit-spawns?

Randomization randomizes the switch to on or off. It's impossible to tell you in the context of a SF map, but yes, you could use it to randomize the guys that spawn. Not many people use it. Check the wiki for more.
http://www.staredit.net/wiki/Randomization
http://www.staredit.net/wiki/Switch
http://www.staredit.net/wiki/Death_Counters

Often switches are used simply to remember that something was triggered, like, in your SF map, chances are, when the player killed a certain unit, or building, a switch was set, and then the map has a trigger that creates units at that building, only when that switch is set.

Switches are generally used for Global events that are the same for all players and can only have 2 values, on or off, if you want to have a variable that's different for every player, you usually want to use Death Counts instead.

thanks for the links... if i knew there was a wiki on the site i would have went there first!

i really like the idea of randomization... it has the potential to make every game you play on a certain map pretty much unique

It says so here...