Read the detailed tutorial here:
https://www.blenderengine.com/post/ad…
In this tutorial you’ll learn to turn the boring flat-looking textures into a 3d realistic look without hurting the performance of your game or rendering time in a very simple and easy-to-follow process, in fact, normal maps are so popular among the computer modelling industry that you can’t not to use them. Normal maps give our textures the depth 3D look on a surface without having to model a surface that adds a whole bunch of extra vertices in our scene, which will pressure the graphics card even more.