I always find many events used in waittill and so on
Is that pre-defined?
and where i could find a list or a explain of the events?

I'm not sure what you mean. Events?

sorry,i am a beginner.I don't konw how to call it exactly.
the events always are used with waittill() func.
For example,Here a trigger_damage.

self waittill ("damage", amount,attacker, direction_vec, point, type);

Here the string "damage", that's what i mean.
my question is :
1.I want to know how and where the events("damage") are defined
2. waittill() is a func?
3.If the string is a pre-defined event(I guess that,because i don't define it as well as the follows var) ,How about other event.
4.The follow var (amount ,attacker...),I dont define them either.
Where to find the declare?

no, there are no predefined "events"

waittill() is a function, built into the game engine

self waittill("damage", ...); will wait until it "recieves" the damage before it continues with the below code

the damage message can be "send" by the following command:

self notify("damage", ...); // i asume "self" refers to the same entity as in the waittill command

Also see here:
http://www.modsonwiki.com/index.php/Call_of_Duty_4:_Scripting_Introduction%23Notify_.2F_Endon_.2F_Waittill