Following on from a Container diagram, 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.
Scope: A single container.
Primary elements: Components within the container in scope.
Supporting elements: Containers (within the software system in scope) plus people and software systems directly connected to the components.
Intended audience: Software architects and developers.
This is an example Component diagram for a fictional Internet Banking System, showing some (rather than all) of the components within the API Application. Here, there are three Spring MVC Rest Controllers providing access points for the JSON/HTTPS API, with each controller subsequently using other components to access data from the Database and Mainframe Banking System, or send e-mails.
The dashed line represents the boundary of the API Application, showing the components (light blue) inside it.