Americans should have greater representation in congress and a multi-party system is what is best for a flourishing democracy. A proportional representation system is a system that can help people in America get the representation that they deserve. This will allow for 3rd parties to gain representation in congress, as well as eliminate congressional gerrymandering in states which has become a big issue in a lot of places.
The proportional representation system works first by parties choosing their candidates. The ones who get the most votes go to the top of a party list. During the general election, votes will be cast for the parties. When the votes are counted, seats will be allocated based on a method called the D’Hondt Method (http://worldheritage.org/articles/D%27Hondt_method#Allocation). The amount of seats for each state will be calculated in the same way (so Indiana will still retain its 9 congressional seats for the 2016 election for instance). So if party A gets 4 of the seats using this method, the top 4 candidates chosen by the party (which for the Republican party will happen through the primaries) will become representatives. The primary will be statewide to allow for a good amount of candidates in each party as well as the elimination of congressional gerrymandering (much like how the senate race does not have to adhere to gerrymandered borders).