There are three notes to learn on the fifth string, the open A note, the B note on the second fret and the C note on the third fret.
The open fifth string is an A note. This A note is written on the second ledger line below the staff.
The note on the second fret of the fifth string is a B note. Use the second finger of your left hand to fret this note. This B note is written under the first ledger line below the staff.
Special attention should be given to the left hand fingering in bar numbers 5 and 6. It is important to hold the B note on the last beat of bar 5 for the entire duration of bar 6. You will therefore need to use the 4th finger of your left hand to finger the G note in bar 6.
The note on the third fret of the fifth string is a C note. Use the third finger of your left hand to fret this note. This C note is written on the first ledger line below the staff.