<p>I have been looking to buy a new extruder. One of the options I have seen comes in "right handed" and "left handed".  What does this mean? How can I tell what my current extruder is, so I get the right replacement?</p>

This is an example of a right handed extruder setup:
And this is an example of a left handed extruder setup:
I believe that you can can choose whatever one you favor. With the right handed setup, you will be pushing down the red part with your right hand when inserting filament. With the left handed setup, you will be doing the same thing but then with your left hand. Personally, I favor the right handed setup (my right hand is my dominant and stronger hand). But, you should be able to choose whatever one you like! Be sure to check it will work with your printer though (extruder holder & hotend).