The lines and spaces that hole the notes
The lines above or below the staff that span beyond your E (4th string, 2nd fret) and F (1st string, 1st fret)
In sheet music for the guitar, you'll see that the treble clef circles the G note
This tells you which key you're in by indicating which notes will be sharp or flat
Notes that don't naturally occur in the key are marked with a sharp, natural, or flat symbol
The horizontal lines that divide the sheet music into measures
There are many different notes, but the 3 most common ones you'll see are whole notes (4 beats), half notes (2 beats), and quarter notes (1 beat). You can keep dividing them down to get even shorter beats. There are eighth notes (1/2 beat), sixteenth notes (1/4 beat), and even thirty-second notes (1/8 beat)
If you are meant to play a note on a certain string, there will be a number above the note telling you which string you're supposed to use. If you are meant to play a note with a certain finger, there will be a number beside the note telling you which finger you should use