Install the recommended extensions. If you closed the notifcation you can find it again here:
Install Docker.
Windows: https://download.docker.com/win/stable/Docker%20for%20Windows%20Installer.exe
Linux: Your package manager should have it.
Run docker run -d -p 8888:8080 plantuml/plantuml-server:tomcat to setup the PlantUML Server
If you install Docker with VSCode running you may need to restart VSCode for the docker command to work.
Ensure each file for projects include .c4.doc.puml to show that it is the c4 level documentation of that file.
Press Alt + D to view .puml files in visualized mode in realtime.
Include .doc.md if you need to elaborate on design thoughts regarding the file. Good notes now make life easier later. Particular implementation details should be in comments in code still.
Press Ctrl + Shift + V to preview Markdown in realtime.
If you need a quick refresher on the C4 model you can check https://c4model.com/.
Cheatsheet: https://c4model.com/assets/visualising-software-architecture.pdf