I'm new to unity and try to put a box gameobject on a plane and be able to move it with the mouse. Everything seems to be there, checked the example project hundred times right now and all settings seems to be identical to those used in the apartment scene.

But, my Cube is not moving. Is there somewhere out there a detailed step by step guide for dummies? I created a plane, added a cube, camera and light. The plane and cube are rigid bodies, gravity is on (and works), collider set (seem to work, cube falls on plane and not trough it).

In some topics I read that the dragrigidbody.js needs to be attached to maincamera, in others people refer it attached to a gameobject, what's correct? How to check what's going on in the background? What am I missing?

Are there project settings to be edited?

Actually, DragRigidBody.js is indipendent from the object you attach it to. That means you can attach it to any gameObject, as long as that gameObject stays on the scene. I usually create an empty gameObject and attach it there, but also attaching it to the camera would work.

Once you attach DragRigidBody.js, all gameObjects with a rigidBody should be draggable. If not, maybe you could post your project somewhere for a quick look?