In order to use it you need to configured in your site configuration (see documentation), in TOML this is basically adding:
[indexes] category = "categories" tag = "tags"
You then add the categories and / or tags per article in the front-matter like:
+++ Categories = ["Hugo"] Description = "Taxonomies in liquorice" Tags = ["liquorice"] ... +++
Liquorice supports either both categories and tags, only one or neither of them.