You currently have 4 pages with a total of 32 storage slots available. With these two buttons, you can switch back and forth between the pages.
A right-click on either button shows you all the pages, allowing you to switch between them more quickly.
Apply your saved colors to the color fields for foreground and background color.
If you hold down the Shift key, the colors will be used in reverse.
If you hold down the Alt/Option key, the foreground color will be applied to all activated layers (shape and text) without changing those colors in your color fields.
If you hold down the Ctrl/Command key, the background color will be applied to all activated layers (shape and text) without changing those colors in your color fields.
If you hold down both the Alt/Option key and the Shift key, the current colors from the color fields will be applied.
If you hold down both the Ctrl/Command key and the Shift key, you can change the saved colors for foreground and background color.
A right-click on a button shows you all available functions as well as additional options, so you don't have to remember the keyboard shortcuts and have even more functions at your fingertips.
In the top right corner of the panel, there is also an export and import function, allowing you to copy your saved colors to another version of Photoshop or create a settings file for different projects.