Originally Posted by Jean Beetham Smith

1) If you are perfect, your leg will be straight, top to bottom. Lots of us don't have perfect conformation (we wouldn't take Best of Show if we were dogs) and may have to deviate from that slightly. The really critical orientation is how much your knee is bent at the bottom of the stroke. Most new cyclists tend to leave their seat too low and aren't able to extend their leg at the bottom of the stroke. Not to confuse you when we get to question 2, but a quick way to check your seat height is to put your heel on the pedal and raise the seat until you are sitting.
2) The ball of your foot should be over the pedal axle.
3) It is the law that you ride with traffic and obey all traffic rules. Riding against traffic is statistically more dangerous.
Welcome to BF. Ride and post regularly. Folks will be glad to help you.