OK. A few clues about diodes.
1. They only conduct one way. The way the arrow on their symbol is. They do not conduct anything (to light a bulb) in the opposite direction.
2. When they do conduct they lose 0.7v across them
3. So if they are in shunt mode (in parallel) with something and conducting, you will not get more than 0.7 across them.
Question 2 is simply Ohms law.
If it's a Zener Diode, then it won't conduct anything until the Zener voltage is exceeded, then it will conduct. The voltage of a series Zener across the load will be your supply voltage minus the Zener voltage. Otherwise it behaves as a normal diode.