can someone post in few short senteces how presidential election in US works? what is going on right now, all those debates etc, how many candidates there really will be. Since you have only two parties (which I think is really bullshit, we have 20+ of them, 5-7 of them have actually chance to get into parliament) , do they have limit for candidates?
As for Presidential elections:
1. 1 term is 4 years. So presidential elections happen every 4 years.
2. Presidents (thu precedent) serve a maximum of 2 terms (8 years total, if relected for a second 4 year term).
3. There are two major parties (Republicans and Democrats). While there is no limit to the number of candidates on the ballot (should you meet the ballot criteria), as well as the fact that anyone can write ANYONE's name on the ballot (called a write-in), throughout history only one candidate from one of the two major parties will be elected president. These parties today are called democratics and republicans.
4. This means, if you want a serious shot at winning, you either need to be the republican or democratic nominee/incumbent.
5. To be the nominee, you need to win the primary election for your party, unless you are the incumbent for the opposing party. An incumbent is the person that currently holds the office, and is running again for another term. In other words, Barack Obama is the incumbent for the Democratic party, hence there is no democratic primary election this time around. He is by default the democratic nominee (incumbent). The republicans must decided for the coming general election (against Obama), who will be their nominee. This is the election process that is going on now in each state (primary elections). The people are voting for who they want as a republican nominee to run against Obama for the general election.
6. Depending on state rules (varies state to state), you may have to be registered as a republican to vote in the republican primary. Other states allow anyone to vote during a primary, regardless or registered party status. (Same goes for democrats if the primary was for the democratic party).
7. If Obama did win the general election, this would be his second and last term. This means in 4 years, there would be no incumbent, and both parties will hold primaries to determine what candidate will represent the party in the general election. If a republican is voted in this year (becomes president by defeating Obama in the general election), then 4 years later the republican president would be the incumbent, and there would only be a democratic primary (as we see now for republicans).