Candidates from each of the parties run in hopes of receiving their party's nomination. If the President is incumbent and would like to run for another term, then the party that he or she belongs to will most likely select he or she as their nomination.
Primary Election and Caucuses are when the voters chose which candidates they prefer, but they also chose the delegates to vote for their candidate at the convention.
The two major parties hold National Conventions which are the meetings that the elected delegates vote to pick the candidates. Since most of the outcomes of the event are known prior, the National Convention is more of a symbolic affair. The convention also serves as a place to present the party’s platform or goals.
When the candidates campaign, they present themselves to the voters, through various forms including; television ads, conferences, newspaper, and dinners. Campaigns are extremely costly which is why only few can afford to run for President.
The election takes place in November every four years on the Tuesday that follows the first Monday in November. It is usually clear who won the election on the night of or morning after the election. But technically the results are not final until the Electoral College votes.
Technically the American population does not vote for a candidate directly. Rather the voters elect an elector who will then vote for a candidate. However many representatives and senators a state has in Congress, is the number of electors it has for the election. A candidate must win 270 out of the 538 electoral votes to become President. After the President wins the electoral college, they are inaugurated into office.