The US Presidential election process is an interesting and complex democratic practice that for the most part matches expectations for the oldest surviving democracy in the world.

The official process begins almost a year before the actual event of electing the president, with the Iowa Caucuses followed by other state caucuses and primary elections that are part of the process to determine which party candidate will win his or her party's nomination to run for President. However one can argue that the process begins more than a year before the main event, when various people begin announcing their candidancies and engaging in lively discusions and debates.

Basically in each US State, each political party, through the process of a caucus or primary, elects a number of delegates for the National Convention of each party that is to take place just before the presidential election. Normally only registered members of the parties can take active part in the caucus or primary process; however, some primaries are "open" in the sense that either independents or even members of the other party can participate. The situation and rules differ from state to state.

Each one of these delegates is bound to one of the respective party's candidates and it is actually the votes of these representatives at the National Convention of their respective party that will determine which presidential candidate for the party will receive the party's nomination. The number of total available delegates is different for each state (basically in direct correlation to each State's population); however, the specifics are determined by processes and regulations particular to each party and in fact the Democrats have a number of super-delegates appointed directly by the party that are there to ensure that the party itself has a significant say in the matter.

Some info on the specifics of National Conventions

The whole process of electing a US President is outlined, step-by-step here

When the time comes for the actual presidential election, each State elects a different number of electors in the electoral college. These electors, collectively, vote for the nominated candidate they prefer for president (the electors form what is known as an Electoral College): electoral votes by state

Here is a nice diagram (with date flags) of an older presidential election process:

The overall presidential election process is stipulated in article 2 of the US Constitution

Some relevant articles at wikipedia

• Presidential Election
• President of the US