Subject: Help with circuit explanation

I have been workin on a project trying to build a circuit with 2 LED's 
wired in such a way that when the current moves in one direction one LED 
light will light and when the current moves in the other direction the 
other LED light will light.  We can use one resistor.  I have done this, 
but I do not know how to explain why it works.  How does the resistor 
change the direction of the current and why does the current only enter the 
negative side of the LED? I know that electrons move from the negative side 
of the terminal to the positive side of the terminal.  THank you

Re: Help with circuit explanation