This article contains information about how to work with 3D vector tiles and Cesium.
For the purpose of visualisation of elevation model, another format can be used, so called Quantized 3D Mesh - the elevation is represented by either regular, but more commonly irregular triangle web.
Sources of 3D data
Have your own terrain data and convert them to 3D quantized mesh format - then you need a server to a) process the data and b) to serve them
Use data provided by the Cesium service
Having 3D tiles data source is only one part of the problem. The 3D tiles will help you just to draw the elevation, but one also needs to “drape” another data source over the elevation, such as the streets map, outdoor map or the satellite map. That way, you can see nice 3D shaped landscape.
Configuring Cesium map application
Check out the tutorial on How to use Cesium JS. This tutorial shows how to create a map and display it on a web page using MapTiler Cloud data.