Whole Sichuan peppercorns are most prominently used in Sichuan cooking where they can be the star of a dish (e.g. mapo tofu). However, the powder form is a central ingredient in the so-called "Five Spices" mix:

- star anise - fennel - cinnamon - clove - sichuan peppercorns

This "five spices" powder is used very often in Northern Chinese cooking as a meat or tofu rub.

In addition, sichuan peppercorns are often used in lushui in the south:

https://soupeduprecipes.com/chinese-master-brine-recipe/

and also it can be found in a lot of braising recipes.