Dude first of all, chill out- if you have just started no one would expect you to match up to one of your friends who has been playing for a while. And to tell you the truth, learning songs is great but if they dont have the knowledge of music behind it, its worthless. So, instead of trying to learn some songs, learn the chords, modes, scales and all that good stuff, and it will really blow ur friends away that you can go on a half an hour rant about how scales and modes relate to making solos while they wouldnt know the difference between major and minor chords. Remember- you are only learning other artists material, not understanding how it was made and therefore not learning how ot make your own. But thats my opinon, if you still want to just learn songs, this is the site i use-
www.mxtabs.com

And about the Green Day songs, all of thier songs are extremely simple to recreate, and none of thier songs have taken me longer than a half an hour, and most you can make out by ear.
Good Luck!! \m/ :D