'if' problem

In fact there are 2 esc's and one servo cause i am building a hover craft.
so in the proggram there are servo1,servo2 as esc and servoWings as actual servo.

Can you exlain to me the example you gave me?

]]servo1.write (signal1 ? 70 : defPos) ;[[

70 is the degrees if signal1 is true? (if signal is 5v)
the question mark what variable is? and the dual dot is something like else?