Mouse

Otherwise known as a computer mouse, is a peripheral that allows users to interface with their computer via two-dimensional pointing motion which produces a corresponding graphical change to the interface. On most systems, this translates to a pointer on screen moving alongside the mouse's motion. It can also trigger further interface options such as opening and navigating menus with use of its button input.

In it's most recognizable form, it is comprised of two buttons corresponding to a left and right, a scroll wheel which can also be pushed down to act as a third button. Originally it had a ball in roller and detects motion with it's movement on the surface. Nowadays mice feature optical sensors with no moving parts. The device has appeared with both wired and recently, wireless capabilities.

DPI

Dots Per Inch refers to how sensitive your mouse is to movement. The higher your DPI, the faster your cursor will move.

The DPI you feel comfortable with is entirely individual, but 400 for lower than 1080p and 800 for higher than 1080p are very common choices.

500Hz vs 1000Hz

These refer to polling rates. 1000Hz is technically more accurate so you might as well set your's to 1000 but the difference is so imperceptible to humans you can't really go wrong with either.