Clef
Bass clef notes
The five lines of the bass clef are G, B, D, F and A, from the bottom up, and the four spaces are A, C, E and G. The bass clef is a stylised letter F. Its two dots sit either side of the fourth line and mark it as F, the F just below middle C (F3).
Read it, then play it
Play the note you see on the staff. The exact key counts: how high the note sits tells you which octave.
The lines: G B D F A
From the bottom up, the lines are G, B, D, F and A. The usual rhyme is Good Boys Do Fine Always. Each line is a third above the one below it, so you are really skipping every other note name.
The spaces: A C E G
From the bottom up, the spaces are A, C, E and G. The usual rhyme is All Cows Eat Grass.
Read from landmarks, not note by note
Start from the note the clef marks: F on the fourth line. From there, every line or space up is the next note name and every one down is the note before. Middle C sits on the first ledger line above the staff.
Above and below the staff
Notes that don't fit on the five lines get short ledger lines. With one ledger line either side, the bass clef covers E2 to C4: 13 white keys on the piano.
How to read ledger lines