First, you need to open the document, then select a text or a table that you want to add shading to. On using the
Format menu, select
Cell > Borders, then navigate to
Patterns (if you want to add or remove Shading). From that menu you can choose the fill method, colors and the style you want to apply it to. Also from the same menu you can work with borders and page borders in case you want to configure something.