Using Patterns
Inkscape comes with a couple of preset patterns. To apply them to an object, you need to:
select the object on the canvas
open the Fill and Stroke dialog, and in the Fill (or Stroke paint) tab, click on the icon for patterns
You will then see a dropdown menu with many pattern names. Select any pattern from the list to apply it immediately to the object.

Object with stock pattern ‘Polka dots, medium’ and a view of the list of available patterns