What lenses should i own?
Focal lengthWide, normal, telephoto, or fisheye? All depending on your preference and what you are shooting. If you can afford it, it is great to have at least 1 selection from each of those categories. Fisheye is typically in the sub 16mm range, wide 17-30, normal 30-60, telephoto 60&up. these are very rough numbers and opinons vary. It also depends on if you have a full frame sensor or a smaller cropped sensor.
SpeedHow fast the lens is determines how much light it can capture. Typically you want the fastest lenses you can afford. Faster lenses can produce shallower depth of field and allow lower iso shooting at night without a flash. Be wary of variable speed zoom lenses, where it may be an F2.8 at wide, but zoom in and it can drop several stops.
Primes vs ZoomsA Prime is a fixed focal length, a zoom is a variable focal length. Primes are usually faster and exhibit fewer visual flaws than zooms, such as chromatic aborations, vingetting, etc.. Zooms are more versitile in that you can think of them as multiple primes, but unless you can afford the high end ones you won't be seeing anything remotely fast.