Speed is about moving as fast as possible in one direction.
Depending on what speed you need to increase, constant repetition of the same movement with little to no resistance will help increase speed. Short bursts and high intensity will help increase as well compared to longer duration and lower intensity. Speed can also be how fast is your movement and repetition. You can move be fast at boxing or able to ski with tremendous arm force that needs repeated motion.
Speed allows you to move quicker from point A to point B with no struggle. This can be very beneficial to sports that require you to travel a distance quickly for a short period.