Just starting out..

ac dc bass lines are easy and super cool

The absolute best thing you can do is find a drummer and the three of you just jam together, you will learn faster this way than by learning other people's lines and you will develop your own style. To start off, have the guitarist jam some chords and get him to call out the chords he's playing and you just play along on the root notes, keep at it and it will grow. There was once a guitarist called Hillel Slovak who asked his school friend, Michael Balzary, if he would play Bass in his band. Michael took the job even though he'd never even held a bass, Michael is better known as Flea these days. Bosh

Play some Metallica. That stuff is typically really easy and then after that you'll be able to have a good foundation for more challenging stuff

Metallica, easy? Not quite. Not for someone just now starting out, anyway.

Drizzt, start with the basics. Stuff every bass player should know, like keeping beat and playing in key. Find yourself an online metronome, practice different speeds, build up your dexterity. Start with easy songs; bands like AC/DC, The Cranberries and Everclear tend to have very simple and easy-to-follow/easy-to-play bass lines. Learn to read tab, learn some basic scales. Nobody's Billy Sheehan or Flea or Les Claypool right out of the gate. Put in the time, master the basics and build from there.

When I first started I did play some Metallica. Kill em All to be more specific. For someone who was starting it wasn't very hard but it was also not really easy. It was an appropriate level of challenge