See installation page for details.
Before starting, just a word to say that you can get more explanation about almost any parameter in Ultimate Terrains just by hovering it (wait 2s and it will display help). This is very useful to get more information about a field without having to go to the documentation all the time.
If you want to see directly what kind of things Ultimate Terrains can do, you can open the provided example scenes (in the folder Assets/uTerrains/Scenes) and just press 'Play'.
You can use these scenes to get an idea of how to setup a terrain, but I strongly recommend that you actually setup a scene from scratch by yourself so you will understand what's going on and what parameters stand for what.
Get a look at our video tutorial (might not be as up-to-date as the written documentation) here: https://youtu.be/gpsxX0kHlHI
See this page page for a detailed, step-by-step tutorial that explains how to setup Ultimate Terrains in a new scene.
Ultimate Terrains let's you configure terrain generation through a node-based editor. This is highly flexible and powerful. A lot of built-in nodes are provided but you can implement your own ones easily.
The Editor tool allows to manipulate the terrain directly within Unity editor. See this page page for more information.
In Ultimate Terrains, real-time modifications are made through operations. See this page page for more information.
Ultimate terrains provides many built-in operations but as for nodes, you can implement your own ones easily. See here to get a look at the source code of built-in operations.
See this page page to see how to save, load and sync terrain data on disk or through the network.