Atlases - how does one use them?

lilweep

for context, these types of atlases: https://www.artstation.com/marketplace/p/pP9n/free-6k-16-bit-atlas-textures-photogrammetry?utm_source=artstation&utm_medium=referral&utm_campaign=homepage&utm_term=marketplace

is this a substance designer thing?

apocalypse_cow

A texture atlas is basically when you put the textures for multiple different objects into one image file (to save file space, usually). Buying a complete texture atlas would only be useful to you if you create yout own 3d models really.