First, install the dependencies. Then run the debug server:
$ yarn install
# then
$ yarn watch
Then, inside the editor, press F5. This will compile and run the extension in a new Extension Development Host window.
VSCode Commands
First of all, you need to open Command Palette (Ctrl + Shift + P). Then few commands will be available to you. You just need to start typing cc, as you can see in the image below.
Both commands do almost the same thing.
Sidebar
The core of the cc @sseraphini extension is on sidebar.
From there you can write your tweet and the extension will do the rest.