I have a Sig Sauer 9mm model 226 pistol. I am new to pistol shooting. This is a silly question - is 9mm Luger the same as 9mm +P ammo?

No. And that isn't a silly question. The 9mm Luger, 9mm parabellum, 9X19, and 9mm NATO are all the same thing.

+P is a designation for an extra hot load that should only be fired in a gun designated for +P loads.

You can also have .38 spl +P loads for example.

I don't own any Sigs, so I can't say for sure. Your particular pistol may or may not be rated for +P loads.

Hope that helps.