I'm new and confused. Does a note mean one string? Is each string a different letter?

The musical staff isn't supposed to be a picture of the guitar strings. It's used for all music, not just guitars. It's more of a grid to visualize notes. Each line and space on the musical staff represents a note. The fact that some are lines and some are spaces doesn't really mean anything. The idea was to make it easier on the eyes. If you're trying to read one note on a musical staff, that means you should play one string. Sometimes letters written above the staff are for guitar chords, which means a whole set of notes in a certain key. If you want to read music, you should also learn some music theory.