i want to make a random number generator that always chooses a number but the number is random

Value = GetRandomInt (1,10)

with Value being your variable name.

And then, after following d4r4dragon's advice, you can do this:

msg (Value)

how can i get a certain number to affect the player

I'm not sure what you're doing here but I assume it's Hit Points related...

player.hitpoints =  player.hit points - Value