Substance designer is all about creating custom procedural materials. You can use baked textures to control how those materials are applied. But generally Substance Designer is more about making tiling textures or procedural content.
Substance Painter is all about working with textures or substances and applying them to a mesh, working with layers, and painting in detail. Substance painter is almost a Photoshop replacement for creating textures for a specific asset. But you can’t make tiling materials within Substance painter by itself. But there is libraries of content online.