e.g. contacts, reminders, messages, notes, etc?
Note that you will be unable to remove an application from the dock if it is open. Click on the Apple logo -> Force Quit if you are not sure if an application is open.
Oh okay, thanks.
How do you remove them?
Either drag the icons from the dock to the trash, or control-click the icon and uncheck 'Keep in Dock'.
This is a useful document from which to learn all about the dock.
Mac Basics: The Dock
Retrieving data ...