If you know how to read tab, Good Riddance by Green Day is good. If you want something easier, Jingle Bells would do.

First of all congrats, pick something simple, pick something you like (you will be playing it for hours on end) go to sheet music direct type in song titles you like and pick the music marked Easy Guitar if you can’t read sheet music order it in tabs (it looks like numbers your instructor can explain this to you)
The first song I could play was Wild Thing, you wont need sheet music for that song, they may start you on one string notes to start as opposed to full chords, look at the sheet music if it is farily simple like the chords are A C D E G you should be good for starters if the chords look like “Bm7 add 9″ it will be difficult for you to start with, look for simple chords.
Other easy chords for beginners are
Am, A7
Bm, (this one is a little hard but you can do it)
C7
Dm, D7
Em, E7
F (this one is a little hard but you can do it)
G7, Gm

try a horse with no name by america. its only 2 chords. and E minor and D6 i think.