How does electron localization/delocalization work? I can't find a simplified explanation on this topic. My textbook just adds to the confusion and all I'm really left with are more questions rather than answers.

And adding to that question, does polarity have an effect on electron localization/delocalization?
Draw the LCAO orbitals.  Delocalization is the summation of discrete electron occupations of orbitals, such as a 1,3 shift (a pi-bond flip).  Remember that LCAO is a terrifically wrong black box. Its only virtue is that it simply, beautifully works (until the Woodward-Hoffmann rules).

Given propene, abstract a methyl proton.  The LCAO anion is half at both ends by a 1,3-shift of the pi bond.  MO shows degenerate orbital occupation still with (nearly) no additional density at the central carbon.  Abstract an allylic proton from 1-butene.  The allylic ends are no longer 50:50 occupied by the anion for the different electronic properties of two attached protons versus a methyl group and a proton.