There are a number of methods in which you can create the geometry that comprise your levels in Unreal Engine 4. Generally speaking, it is better (more efficient performance wise) to use Static Meshes when creating the geometry.
That said, since creating Static Meshes requires some sort of 3D modeling software, you can use the Geometry Editing tools to quickly block out your levels for gameplay prototyping.
This page covers the Geometry_Editing map and illustrates how to begin blocking out levels by using Additive and Subtractive Brushes to define the areas where geometry exists. By the end of the examples, you will learn how to build a house entirely out of Brushes and should have enough knowledge to start blocking out your own levels.
You can find additional resources about each example by clicking on the example's name in table below.