When choosing a lens for your dslr camera, things can get out of hand quickly. There is so much to choose from, and so much to do with different type of lenses, that it can be really daunting to make the right decision. Good lenses aren't cheep, so you'll want to invest in a lens that you will actually use. The main distinction are prime lenses and zoom lenses. Prime lenses have a fixed focal length, while zoom lenses do what the title promises, they zoom in and out out of various focal lengths.
As a photographer it's important to know what you will be using your lens for, so in that sense it's good to take a look at the various types of lenses so that you can make an informed decision.
Fisheye (12mm or less)
Wide Angle (18-30mm)
When you use a wide angle lens, simply know the image will distort and the depth will be exaggerated so you can use it to your advantage.
Standard (35-85 mm)
Standard lenses mirror what the human eye sees most closely. If you want your photos to look natural, standard is the way to go. A 50mm lens is generally considered to be the closest to what the human eye sees, although some will argue a 35mm is closer. Regardless, both produce beautiful, natural-looking photographs. Additionally, 35mm, 50mm, and 85mm are common focal lengths for inexpensive prime lenses (especially 50mm). This is great because it's a way to find lenses with wide maximum apertures (e.g f/1.4, f/1.8, f/2, and f/2.8) without spending a lot of money. If you're looking to take portraits or close-ups of nature, a 50mm offers the most options. Many prefer 85mm for portraits, however, as it flattens the depth of the image even more (and depth isn't particularly flattering to the human face, just look what a fish eye lens does and you can see). Regardless of what you choose, everyone should have a lens in the standard range. While they may not offer special features, they're rarely a bad choice for most types of photos.