Where can you find number formats?

On the home tab of the ribbon, you’ll find a menu of build-in number formats. Below this menu to the right, there is small button to access all number formats, including custom formats:

This button opens the Format Cells dialog box. You’ll find a complete list of number formats, organized by category, on the Number tab:

Note: you can open Format Cells dialog box with the keyboard shortcut Control + 1.