Static structure diagrams
Structurizr supports four types of static structure diagrams. These are the System Landscape, System Context, Container and Component diagrams; a simple hierarchy of diagrams that can be used to describe the static structure of a software system.
System Context diagram
A System Context diagram is a good starting point for diagramming and documenting a software system, allowing you to step back and see the big picture. Draw a diagram showing your system as a box in the centre, surrounded by its users and the other systems that it interacts with.
Detail isn't important here as this is your zoomed out view showing a big picture of the system landscape. The focus should be on people (actors, roles, personas, etc) and software systems rather than technologies, protocols and other low-level details. It's the sort of diagram that you could show to non-technical people.
Once you understand how your system fits in to the overall IT environment, a really useful next step is to illustrate the high-level technology choices with a Container diagram. A "container" is something like a web application, desktop application, mobile app, database, file system, etc. Essentially, a container is a separately deployable unit that executes code or stores data.
The Container diagram shows the high-level shape of the software architecture and how responsibilities are distributed across it. It also shows the major technology choices and how the containers communicate with one another. It's a simple, high-level technology focussed diagram that is useful for software developers and support/operations staff alike.
Next you can zoom in and decompose each container further to identify the major structural building blocks and their interactions.
The Component diagram shows how a container is made up of a number of components, what each of those components are, their responsibilities and the technology/implementation details.
The example diagram you see here is a Component diagram for the Spring PetClinic and the collection of components has been automatically extracted from the codebase using static analysis and reflection techniques. The full-size diagram can be found here.
System Landscape diagram
The System Landscape diagram is really the same as the System Context diagram, without a focus on a specific software system. It can help to provide a broader view of the people and software systems that are related to and reside within a given enterprise context (e.g. a business or organisation). The following diagrams show an example of this.
This is a System Landscape diagram for a fictional business called "Widgets Limited", showing the people and software systems related to the business.