It allows you to pick both your departure and desired arrival airports, lets you select dates for the flights, shows you comparisons with competitors prices below (so if you don't like/trust a particular company, you can simply see what another airline would cost), and much more. Perhaps the best parts of using this tool, however, are the ability to see a range of prices for the same flight for the next two weeks, and the world map, that highlights surrounding flights and prices. These two functions alone make it the ultimate planning tool. If you don't know where to travel, but have a small budget, you can simply pick ur current location and look at the cost of flights around the whole world. If you want to fly somewhere, but are worried that the price might be cheaper in a few weeks, after spring break ends, you can see up to 2 weeks in advance of the date you selected. Maybe you wanted to fly somewhere like Boston, but realized that a flight to Manchester was over $100 cheaper and the same distance from home (Maine)?
HOWEVER, this isn't the final step to finding the cheapest flight....Once you've found a particular flight, then you can use sites like cheapoair, kayak, expedia, etc...The reason that this will save you more money as opposed to simply using the discount rate sites to start is because of the above mentioned functions on google flights. Having the ability to see if the flight might be cheaper a week later is only possible by looking on google.com/flights first and then purchasing on cheapoair. Otherwise you have to spend all nights changing the dates on cheapoair, and checking a nearby airport one day and place at a time.
*Note this is only intended to help you FIND the cheapest flight. When it comes time to purchase the ticket there are all kinds of ways to sign up for credit cards with free miles, or things similar, to help save money. Nomadic Matt has another great blog regarding this here.
If you have any additional tips regarding cheap airline tickets please leave a comment below.