Pedals not turning together I have just tried to tighten up the nuts at the end of my crank but for some reason the pedals don't work in unison and now the left and right pedals are at a 90 degree angle instead of 180 and I'm not sure what's wrong.  How could I fix it?

Think of it as instead of one pedal being at 6 o'clock and one at 12 o'clock like normal, one is at 12 o'clock and the other one is at 3 o'clock.
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.