To use the toolbox, including cbuild, csolution and cpackget , you need to install several extensions:Arm CMSIS Solution, Arm Device Manager, Arm Keil Studio Pack, and so on.
And you need to install the toolbox following the link, I recommend you install it in vscode. It not only installed the toolbox itself, in my computer, when installing the toolbox by vcpkg, it also installed the flowing packages, 
after installing them, you need to specify some environment variables to make sure the project building is successful but do not worry if you install the toolbox in vscode, it will raise a window with tips.
Maybe it works now, but for me, it did not, I need to modify csolution.yml file to select a compiler with help of document and update the cmake to support.
Now it works.
I think it's difficult to use it.
Installation is easy, but after creating a project, compilation, and reconfiguring are difficult
And I think it's not created for people to use but for tools, like Keil(I guess), because if you obverse the project in Keil, you can find the uvoptx file is a xml file.