If you don't want to use any terrain generator feature, just follow these steps:

1.- Create a new scene and add VoxelPlayEnvironment (menu GameObject -> Voxel Play -> Create Voxel Play Environment).

2.- Create a new World Definition (right-click on your project panel, select Create -> Voxel Play -> World Definition).

3.- Assign the World Definition to the VoxelPlayEnvironment inspector's "World" field.

Run the scene. You will get a fully functional voxel engine with no predefined terrain.