This repo has examples of PlantUML code and diagrams, along with some coding hints and a few other bits and pieces.
PlantUML has multiple types of diagram, however rather than explicitly specifying the type in code, it is implied by the choice of the first unique object specified... Or by the @ directive at the start of the code (examples: @startmindmap, @startgantt, etc.). Click the link below for more on this, including the built-in diagram types:
Different types of object, including actors, components, interfaces, rectangles etc.
Different types of line
How to apply visual styles diagrams
TBD - scale diagram with zoom. see: http://plantuml.com/commons
Headers, footers, legends etc.
All skinparams: https://plantuml-documentation.readthedocs.io/en/latest/formatting/all-skin-params.html
Interview with Arnaud Roques (creator of PlantUML): https://modeling-languages.com/interview-plantuml/
Blog post by Alex Sarafian with some good PlantUML tips and tricks https://sarafian.github.io/tips/2021/03/11/plantuml-tips-tricks-1.html
https://github.com/joelparkerhenderson/demo_plantuml