There isn’t a single popular vote. There are 538 votes to be cast, votes distributed to the states based on the most recent census.
Each state then runs an election to determine how their vote is cast. More technically, you’re voting for a specific elector, but given faithless elector laws, it’s defacto a specific candidate.
Most states are all-or-nothing, whoever wins that state gets that state’s full vote count.
To win, it takes 270 electoral votes.
This is why battleground states are so important. Hillary may have gotten more votes nationally, but none of the elections were in fact national. She ignored key battleground states and arrogantly expected to just win them.
Hillary was, and remains, an arrogant fool. Not, it must be said, in the same way Trump is.