What is the use of substance painter?

The use of this software is to make the different texture maps of some 3D model adding effects to them for greater detail and realism to the 3D model with effects ranging from luminescence, normal maps (reliefs), opacity, light maps, with Over time, more advanced options were added, either to interact with the object, make scenes, etc.

it is used to paint 3d models made in any modeling software like blender or 3d Max.

Substance painter is a tool used for texturing 3D work, for example you may have a 3D model of a table and you want it look like an actual real life table, with substance painter you can use wood textures to add to the model so that it looks like something made from real wood. The app is commonly used by game developers , videographers and 3D artists