An opamp needs a little power to operate, so most of them never get quite out to the V+ and V-. Those are the "power rails". SOME can operate very close to the rails, however!
An amplifying device can only give out as much as is put in - by the input signal and the power supply. You are using the input signal to control how much of the power supply becomes the output. You can't get more out than there is to offer from the power supply! That would violate the laws of conservation of matter, LOL.
Check out the E-books on here, and use Google to look up "amplifying device tutorial", "opamp tutorial" and the like. There is much information about this out there, for free! )
by Duane Benson
by Jake Hertz
by Aaron Carman