Beer has not always contained hops. Before the use of hops began in the 11th century, people mostly used a combination of herbs and spices known as gruit, to bitter their beer. There was no standard way of bittering your beer and everything from mugwort to heather was used to take the edge off the sweetness of the brew.
Over a period of a few centuries, hops were introduced to everywhere brewing took place and they swiftly replaced all of the previously used bittering agents.
There were several good reasons for this; hops do the job of bittering much better than any other additive, hops act as a preservative, so breweries don't have to worry about beer spoilage as much and arguably most importantly, hops have a pleasant flavour and aroma when used in beer, so customers prefer hopped beers.
Over the centuries hops have been selectively bred, in many parts of the world, to adapt to local conditions and bring out locally favoured characteristics. They went on to become essential elements of the local beers and help to define every style of beer you care to name.
In these days of international commerce there is a huge variety of vastly different hops available to the craft brewer. Spicey Saaz from the Czech Republic can be bought from the same shop that sells citrusy American Cascade and floral English Goldings.
They are so much more than just a bittering additive; they are essential to the character of almost every beer style. So much so that the same malt profile can be turned into many different beers, with the careful application of the right hop, or combination of hops and as such they are quite possibly the most versatile tool available to the brewer, especially the extract brewer.
If for example you have 3Kg of dry malt extract and a bit of crystal malt for steeping, there are many styles you could make.
If you get some Cascade, Amarillo, Chinook, or other fruity American hops you can make a distinctive American pale ale.
If you go for Fuggles, East Kent Goldings, Target, First Gold, or other English hop, an ESB can be made.
Choosing Tettnanger, Hallertauer Mittelfruh, Saaz, etc, can turn this into a lager (or lager like blond ale, if a clean ale yeast is used instead of a lager yeast).
So be glad that you live in a time with such a wonderful selection of quality hops available. Use them singly, or in combination with other varieties, to create distinctive flavour and aroma experiences.