There are at least two ways to look at this question.
First, we can look at the technical steps one must take to become president. A person must declare their candidacy for the presidency. Then (for the people who have any shot at becoming president) there is the primary election. Each candidate must vie to be selected by one of the two major parties as that party’s candidate. Next comes the general election. The winning candidate needs to win a majority of the electoral votes cast.
Second, we can look at this as a question about what a person has to accomplish in order to be a credible candidate for the presidency. Here, the answer is less clear. Four of the last six presidents (Carter, Reagan, Clinton, George W. Bush) have been governors before they became president. It is believed to be important to have that sort of executive experience in order to be president. If you have not been a governor, you at least need to have been in high office. No president outside of Dwight Eisenhower in the last 100 years has made it to that office without having been in high office before.
Outside of that, it is an issue of having two things. First, you need to have some amount of charisma that makes people think that you will be able to get elected and do a good job. This allows you to raise enough money to do the second thing. The second thing is to have a really good organization that can help you to identify people who might vote for you and persuade them to actually do so.
This is, of course, a terribly truncated discussion of all of the factors that go into becoming president, but the basic idea is that you have to have some combination of fame, charisma, and organization to become president.