In order for Indie to be able to show you a price, it needs to know when you are going to travel. If your flight dates fall outside of the 11 months time frame for which airline offers availability, you can use "mock up" dates (any dates within 11 months of the day you are pricing) to get an idea of how much the trip could cost.
Indie searches over 500 major airlines and low-cost carriers to find you the cheapest seat on a plane for the day you are traveling.
Once you have a price, you can start changing the dates to see how the price changes. We often find that flying on a mid-week day (Tuesday to Thursday) is a cheaper option.