PS CS2 and straighten

[Lensmeister]

I posted in one of the galleries a photo and someone said I should straighten the horizon. so I haeve two questions.

1. How?

2. if I straighten the horizon will it make any vertical lines lean or look not straight ?

Please help .

 

[woodsac]

Under the eyedropper tool is the straighten tool. Looks like a ruler. Use it to draw a line across the horizon. Then go Image>Rotate Canvas>Arbitrary. It wall automatically determine the amount and direction. Click ok.

As far as vertical, yes. It's going to rotate the entire image