Although it's not necessary to "sight read" music (unless you're planning to become part of an orchestra or a studio session musician) I think that it's important to have a few notions about notation and be able to recognize notes and divisions. I will use notation in the site in the Theory section and alongside Tabs for exercises and techniques so bear with me, it won't be that tough to learn the basics.
Notes are written on a Staff (sometimes more than one) which is a system formed by five lines and four spaces with a Clef symbol at the beginning. The clef determines where the notes go on the staff and different clefs are used for different musical instruments due to their note extensions.
Below we see the Treble or G Clef, it's the most common clef and it's used for violin, vocals, the right hand of the piano and (improperly, as we'll see shortly) for guitar.
It's called G Clef because the center of the spiral in the symbol indicates that G above middle C is on the second line from the bottom of the staff (also the symbol itself is a stylized capital G). Middle C is a C roughly at the center of a piano keyboard (or approximately 262 Hz) and is a reference point for notation: in these digital times it's also called a C 3 (a C in the third octave of the MIDI reference system).
After the Clef we find the time signature that define the meter of the music. Music is divided in uniform time sections called bars or measures, and time signatures establish the number of beats in each. But more on this later.
Let's begin to put some notes on the lines of the staff. We already know that the G above middle C goes on the second line so descending from that we'll find an E on the first line and a C (middle C or C 3) on a little line that's called a Ledger and is used to extend the Staff above and below the five lines. On a second Ledger we see an A and on a third an F. Getting back to the G and going upwards we have B, D, and F on the next lines and A, C and E on the upper ledgers.
The missing notes are written in the spaces between the lines. In guitar notation the E under the third lower ledger corresponds to the open sixth string and the C in the second space from the top is the C on the first fret of the second string. This poses a problem since, as far as pitch is concerned, this note corresponds to middle C....
So guitar music is actually notated an octave higher than it actually sounds or it would extend so much under the staff to make it virtually unreadable or require the use of another Clef. Actually it's not unusual to notate an octave higher or lower that the actual pitch but it's usually indicated by a small 8 over or under the Clef: by convention guitar notation does not require this. We'll see later that a special symbol is used when the notes are too high to be notated with a reasonable number of ledgers.
For bass guitar and other low tuned instruments (including the left hand on a piano) we use a Bass or F Clef. Note how the two dots in the Clef symbol frame the second line from the top and strangely enough on this very line we find the F below middle C. This means that the C on the first high ledger is middle C.
We can join the two Clefs at middle C and see how they flow one into the other.
We won't have to bother with the Bass Clef in guitar scores too much (if ever) but we'll have to consider sharps and flats (the black piano keys): on the next page we'll talk about accidentals and how to insert them in our scores.