There are many types of diodes and it would take a lot of time to explain them all.
Plus this http://en.wikipedia.org/wiki/Diode and googling will help you better.
I used to solve circuits 2 years ago, I barely remember them. But if you post your circuit I might remember.
been a while since ive worked on the theory, but you should plot the load line for the circuit choosing different value for the diode voltage (this should be linear) against the characteristic curve of the diode.
let me google an example