Unreal Engine's Navigation System provides pathfinding capabilities to Artificial Intelligence Agents. To make it possible to find a path between a start location and a destination, a Navigation Mesh is generated from the world's collision geometry. These guides will teach you how to modify the Navigation Mesh generation in Unreal Engine.
The Preparation Guide will create the sample Level required to follow the Modifying the Navigation Mesh guide. Alternatively, you can download the full sample project, which includes the completed Level named LevelMod_Navigation_0.