The Electoral College is the defining process behind the election of a US President. That check on the excesses of democracy put in place by the Founding Fathers dominates discussion of presidential elections because ultimately however many votes you win won’t help you if you can’t convert it into electoral college votes (just ask the Bull Moosers in 1912…)
The Electoral College is one of those concepts that you either get instinctively or you sit there puzzling at it for ages and still end up a bit confused. If you fall into the later category this excellent little video from the Economist is ideal if goes through how the Electoral College functions with little animated diagrams. What more could you want from an explanation!