Bear with me on this one - it is somewhat complicated and I'm being careful not to pass on any misinformation. If any of what I've written below is mistaken, please let me know as soon as possible and I will rectify it.
Inside Iraq, people will vote for a national assembly and a provincial council (the Kurdish areas will vote additionally for a separate Kurdish Parliament). Outside of Iraq, Iraqis will only be able to vote for the national assembly.
Across the country and in member voting countries, voters will have the same ballot for the national assembly. In Canada, by contrast, you vote for whoever is running in your district.
The system being used is called proportional representation. What does this mean? Generally, if a given party gets, say 20% of the vote, then that will be represented by the number of seats on a percentage basis : 20% of the 275 seats = 55 seats. Additionally, there is a mandate to have a representation of at least 25% women in the National Assembly.
Proportional representation, it is argued, is needed in Iraq to allow the smaller parties a stronger chance of winning seats. Conversely, candidates who may be very popular in specific geographical areas will dilute their chances to win seats.
Hence, the need for coalitions. A single candidate has litle chance for winning a seat if he/she runs as a single entity. Even if the candidate's platform is popular, one seat will need at least 40,000 votes.
More in-depth info can be found at http://www.ieciraq.org
This national assembly is considered transitional. The two key duties of the National Assembly is to 1) appoint government ministers, including prime minister, and 2) draft the permanent constitution of Iraq (which will be presented to Iraqis in a referendum).