Procedural Plastic Materials
How I can turn on materials displacement?
Because these materials use displacement, and in material setting select Bump and Displacement to get accurate results.
Subdivide your mesh to see displacement.
How I can add materials in my .blend files?
You can append materials from purchased file to your files.
Which Coordinates are best for these materials?
You can use UV or Object coordinates. When your object is UV unwrapped then use UV coordinates otherwise use object coordinates.
You can change it in nodes setup in texture coordinate node.