The Cloth Library Addon works in two modes. Premade mode is a collection of ready-made cloth garments that are one click away and made to work with your model. The premade pose mode lets you select an asset and pose the garment to match your model's pose.
The simulation system comes with its own library, this time of sewing patterns that work with Blender's internal simulation system. Pick the type of shirt you want from the categories and the addon links the suitable sewing patterns into your scene. Align them with your character, press play, and use pattern mode to move, rotate and scale patterns or shift individual ones with the pattern controls.
A male and female model are packed into the addon, so enabling the use pose dummy option matches the pose and means clothes don't need scaling, with collision already set up for simulating directly onto that mesh. Custom models work too once their collision property is turned on. Sculpt mode covers both premade and simulatable assets, with a cloth brush in the post simulation panel for adding extra wrinkles. A December 2022 update added 24 cartoon and stylized cloth items with 4k PBR textures.