The mouse cursor is key in helping users understand how to interact with elements on the screen.

Default cursor: cursor shown by default.
Pointer cursor: used to indicate that you can click on an element to invoke a command or navigate, such as links and buttons.
Grab: indicates that you can grab and move an element around the screen.
Grabbing: indicates that you are actively moving an element around the screen.
I-beam cursor: indicates that this is either text that you can select and copy, or a text field that you can click into to enter text.