Pedals not turning together
Did you take one of the crank arms off at some point?
Did one fall off accidentally?
Or is someone playing a trick on you?

Remove dust cap if its in the crank's axle.
Unscrew the nut of the left side crank, probably a 14mm socket.
Take the pedal crank off - it should be really hard and you need a crank puller, or it will be suspiciously easy.
Put crank arm back on so its the right position compared to the other side.
Reinstall nut/bolt and tighten it up good and tight.
Reinstall dust cap if you had one.

I've been guilty of doing it wrong... mostly because of working later at night when tired.