What does x mean to do when it's in front of a note in sheet music?

I believe it means to raise the note a semi-tone. So if the not was F# with the x in front, you need to really press G.

It's a double sharp, and raises a natural by two semitones (or two half steps). For example, an "x" in front of an F would be played two half steps higher than the F, and would be called F double sharp - enharmonically the same as G.

thanks for the correction..I am very rusty and wasn't sure if it was 1 or 2 semitones.

No problem. Don't feel bad. This is probably one of the most-asked questions in the Pianist's Corner.