The presidential race is the competition between people who want to become President of the United States. People who have similar ideas belong to the same political party and campaign through a series of events called Primaries and Caucuses. These events lead to a selection of delegates who will represent the people at the party convention. Once the delegates have chosen their final candidate, they “endorse” them to go forward in the general election. The candidate who wins a majority of the votes (270 or more) is elected as President. They also select a Vice President.
The race between Trump and Biden has been unusual. Biden has had a long and distinguished record of public service while Trump, a billionaire businessman with no prior experience in government, flirted with the idea of running for decades before finally deciding to run in 2020.
Both candidates have a wide base of support from both within and outside their political parties. However, the Democratic candidate has an advantage in that he has the support of many unions and left-leaning organizations.
The electoral college system in the US can produce unexpected results. For example, last year, Republicans gained seats in the House of Representatives despite predictions of a blue wave while Democrats lost a number of seats in the Senate despite the fact that Kamala Harris had more national support than Donald Trump. The difference is largely due to the fact that voters in early-voting states like Iowa and New Hampshire often have a much greater influence on the outcome of the contest than voters in California and other late-voting states.