When modelling for game engines, one of the main goals is keeping the poly count low. In the same time, we all like detail into the models so one technique to meet these two criteria is the use of normal maps (or bump maps). Here is a tutorial on how to bake the normal map from a high poly count model and use it on the low poly model, to visually obtain a similar looking asset.
Because the previous tutorial has been removed here is an equivalent version. A tutorial on the 2.79 always interesting from a theoretical point of view (see the 3rd video for normal map) https://www.youtube.com/playlist?list=PLvvt6JsSMTGlbVMLk0aUdtEFaaLtmjcOy
