A system in which the candidate who receives the most votes wins. In contrast, proportional systems allocate votes to multiple winners. (states that use proportional systems include Nebraska and Maine-only 2 that do). The candidate that receives the largest popular vote in a state is credited with all that state's electoral votes.
After the general election (Nov) in December, electors (repub or dem, depending on which candidate has won the state's popular vote) meet in their state capitals to cast their votes for president and vice pres. It is not a requirement for electors to vote the way of their state's popular vote, but it is known if they do (names are published in paper). This doesn't happen often, but it's not illegal. Everyone gets their vote (drafted in the constitution).
The electoral college ballots are sent to the US senate, which counts and certifies them before a joint session of Congress held in early January. This is how we declare who is president.