Classical guitarists are no different from other musicians dealing with written music in that after they identify and understand the symbols of standard music notation, they have to correlate them to their instrument. In other words, they have to play. At the most basic level — executing the correct pitch and rhythm — you must be able to play the note you see on the staff correctly on the guitar.
Associating a note on the staff with a string and fret location (even if the fret is zero — meaning an open string) is the first step to reading music on the guitar. A good way to begin associating notes on the staff as they relate to the guitar is to consider just the pitches of the open strings.
The diagram above the staff shows the guitar neck if you were to hold it upright, facing the headstock, with the low E string appearing at the far left.
You can use these pitches to help tune your guitar to a piano or other fixed-pitch source.
To help you correlate the notes of the treble clef with the frets on the guitar, check out notes E to F on the staff as they correspond to the fingerboard. Don’t worry about playing anything yet — just get used to the idea that when you see, for example, an E on the 1st line of the treble clef, it corresponds to the 4th string, 2nd fret on the guitar.
Though the notes can extend off the staff in each direction by at least three ledger lines, in reality you’ll encounter far more passages of notes using ledger lines below the staff than above it. So be sure you get familiar with those low pitches, as you’ll be playing them quite a bit.