Question:   What is the difference between polar and nonpolar?

Answer:

When things are polar, the electrons in the thing spend more time in one place than another.  For example, if you have a polar covalent bond, the shared electrons in the covalent bond tend to like to spend more time hanging around one atom than the other.

Polarity is caused by differences in electronegativity - basically, electronegativity measures how much an atom likes to grab electrons.  If an atom that's not electronegative (doesn't want to grab electrons) bonds with one that is electronegative (it wants to grab electrons), the electrons will gravitate toward the electronegative one, making the bond polar.  If one of the atoms is very electronegative and the other has a low enough electronegativity, the electrons will transfer from one atom to the other, causing the formation of an ionic compound.

For some practice worksheets about polarity, click HERE and HERE.