The first step in creating good diagrams is simply to copy an existing one faithfully. Use draw.io to reproduce the diagram below.
The links below lead to ER diagrams which are not in UML format. Use draw.io to produce a UML version of each one.
3. Problem solving
The diagrams linked in this section all have something wrong with them. Write down as many problems as you can identify - some diagrams may have several issues. When you have done that, use draw.io to create a correct version of each one.