Most likely it's the battery. There's enough juice to get the lights on but not enough to start up the car. Get a jump start. If that starts the car up, then there's your answer.
Car Won't Start But Ignition Lights Come On, Can You Help?
I'm having the same problem, but... It's the starter, the car was fine last night, but this morning it wouldn't start. I tried jump starting it, than tested a different battery in the car... And none of them worked, so that ruled out the battery... So I changed my starter and it's fine again... Try banging on the starter a few times than starting it... Might work temporarily.
