Clothes are one of the items slowly used up by villagers.

Clothes can be crafted after researching tailoring.
Workshops can craft clothes from fur or fabric.
For a comprehensive guide to obtain clothes, see Tools.

Tailor can craft clothes from fabric cheaper than workshops.

Villagers use more clothes if the temperature is lower (only in winter).

Fur can be used as less effective clothing for villagers by selecting option in management, but this was bugged, so that the villagers would continue to have the debuff to happiness from using improvised furs as clothes (Fixed in v1.3.9 according to changelog).

They are one of the things you should try to get when in the early game.