You can find a detailed guide to add new keyboard shortcut over there in "Adding a Custom Keyboard Shortcut" section.
Quote with a quick description:
Most "custom" shortcuts are used to launch specific applications, so I
will describe the process with that goal in mind. To add your own
keyboard shortcut for an application, go to the "Applications Menu
Definition" panel in the Preferences app. Select the application item
in the menu for which you want to create a shortcut, then use the
"capture" button to capture the keystrokes you want to assign to that
item.