I have a switch that controls the outside garage light and would like to put an outlet next to it. The switch has a black wire and a wite one marked black. So do I just add the switch in to the hot (black) wre then make a "jumper" wire from the white side to the black hot side of the switch, and leave the white marked black on the other side of the switch. Does this leave the outlet always on, even when switch is off?
:confused:

If you only have a black and white at switch, no.
If that is the case, However at the light you likely have a hot, neutral and switched leg for light. The receptacle if wired from light box, receptacle can be live all the time or work only when light is on.

In a garage you can wire it so the outlets are hot when lights are on -- or wire it so

The outlets are hot all the time... You just get power after switch for switched power

And before the switch for constant power... You can also have both switched and

Non switched outlets if you chose... Like to have radio on switched outlet...