uml – How do I represent external systems, functions and data in class diagrams?

I have an exam and the questions are, (the answers could be "not at all", "none")
1. How are the functions shown in the class diagram?
2. How is the data presented in a class diagram?
3. How will external systems be represented, which means people and technical systems outside the modeled system?
4. What relationships between functions are represented? (Answer with short sentences like "A call B above"). How are these represented? (Draw or describe, for example, "dashed line with open arrowhead from A to B").
5. What relationships between data are shown? How?
6. What relationships between external systems are represented? How?
7. What are the relationships between functions and data? How?
8. What are the relationships between functions and external systems? How?
9. What relationships are represented between data and external systems? How?
Thanks in advance for the help.