My 2001 Hyundai Elantra won't start. The engine makes a clicking sound

[curious]

but won't turn over. Why? What would cause it to do this? I got a jump and now it runs but I don't want it to happen to me again.

[pink]

it is either battery or solenoid.

[idk]

BATTERY!
Did you leave a car door open for a while?
Jumping saved you. Luckily, it wasn't completely dead. Watch out next time. Or just replace it with a new one.

[An Asteroid]

Your battery was very low and not supplying enough juice to make the starter go. The click was the starter solenoid engaging,

Bring it to AutoZone and they will test the battery and alternator for free. Many other parts stores do this as well. If it tests out OK, you just left a light on or something, or your charging system is going and your battery didn't get a good charge.

If either is bad, you need to replace one or the other. The alternator is buried on this car (great engineering - bury the part that fails more frequently and cost the owner hundreds in labor to save $0.83 at the assembly line) and will require much more labor to replace than it should. Plus the alternators are expensive, so you could be looking at over $500 for a fix (a reasonable shop will charge less, so search around for a good price).