ELI5 How someone can get the majority of American's to vote for them by winning the popular vote but still lose the election? Kind of like Hillary did?

In each state you only need >50% of the votes to win all the electoral points for that state. Once you have 50% of the votes in a state, additional votes within that state are essentially worthless. In Hillary's case her supporters were heavily clustered in a handful of states. She won California by a landslide, for example, but then went on to lose in a bunch of other states by narrow margins. If her supporters had been spread out among more states she would have easily won the overall election.