Get out your notepad and lick the end of your pencil because you're about to experience the 101 class on wood flooring. Of course considering space is short, this will be the much abbreviated 101!. (I can hear the rejoicing.)
Let's look at the most popular flooring choices so you can at least focus on trying to find out what's best for your project.
Let's talk wood. There are five main types of "hardwood" floors: solid hardwood, engineered wood, parquet, laminate, and vinyl "wood" flooring. All of these types come to us in the form of a "plank," or an elongated piece (with varying width) that is now typically equipped with tongue and groove or an interlocking mechanism to make installation easy. The floors can "float," which means they are not actually attached to the sub-flooring and are just locked together, and trim or quarter-round holds the floor in place, or they can be glued or nailed down.
As a sidebar here, bamboo is becoming a very popular material used as "hardwood" flooring. It is not wood, however, but is actually a grass. It can be made into terrific, wood-like flooring that is strong and durable, and even better, the grass grows very quickly and is readily available, so it's an eco-friendly product as well.
Solid hardwood is just that, a solid piece of sawn hardwood, cut into planks. This style is very popular and has been used for centuries. It's long-lasting and beautiful, but it does take careful maintenance over time, and it is not recommended for use over concrete sub-flooring.