And just like that, you're already practically through the "meat" of this thread. The next string here is the A string; the 5th string.
The 3 notes which you'll learn for the A string (to start off) will be the open note, the 2nd fret and the 3rd fret — which are the A, B, and C notes respectively.
The first note, the A note, is played on the open string
The second note is the B note, played on the 2nd fret of the 5th string
Finally, the third note is the C note, played on the 3rd fret of the 5th string
Here's your exercise to become more familiarized with the A string's note names. Like before, a couple songs are coming up next that use the A string.