The diagram below shows you all of the primary notes on the fretboard of the guitar. You’ll use it in order to identify the name of the key signature. In order to get a sharp (#) simply go up one fret. To get a flat (b) just go down one fret. For example F# (2nd fret, low E string) would be one fret higher than F (1st fret, low E string).
Now I don’t expect you to memorize the notes on the low E string in 30 minutes or less. All you really need to do right now is print out our cheat sheet. I contains a notes on the fretboard diagram. By using the diagram you can easily find the notes on the low E string.