To use root motion, first you need to create a character with a walk or run animation, that has translation in it; see the following screenshot:

If you are using a Humanoid character, the hip bone is used as the root node, the one describing root motion. So hip translation will describe the translation of the character in game (you can still have motion in the Y axis as we can then adjust it in the Import settings). Its rotation will describe character rotation in the game. If you are using a Generic character, you need to choose the Root Node manually in the Import settings. Select the model, go to Inspector, click on the Rig tab, set the Animation Type to Generic, and select the Root Node from its drop-down menu (it contains the whole bone hierarchy of your rig).

You can also download the provided example Unity project and go to Chapter 04 Character movementRecipe 02 Using root motion to drive rigid body characters movement with animations directory. You will find a scene called Example.unity there, with a Humanoid game object in the Hierarchy.