US voters directly elect members of which branch of the federal government?

Voters directly elect their congressman and senators, who form the legislative branch. The person who wins the most votes in a state wins the election.

Voters do not technically elect the president. The president is chosen by the electoral college. People vote in the presidential election and their votes are tallied by the states. Each state has a certain number of electoral votes. If 51% of the people of Florida, then all of Florida's electoral college votes go for that person. At the end of election day, all the votes are tallied in each state, and the electoral college votes numbers are added up. Whoever wins the majority of the electoral college wins.

This means that even if a candidate wins the majority of votes, as Al Gore did in 2000, he can still lose in the electoral college and lose the presidency.