First, download the appropriate installation package for your operating system from the Download page of VirtualBox.
Next, we install VirtualBox (at the time of writing, it is version 6.1.12). In the individual installation steps, we can simply accept the default values and literally click our way through. We may be asked whether an additional network adapter should also be set up: we confirm this with "install".
When the installation is complete, we can leave the "start after installation" checkbox checked.
For me on Windows, an additional network connection has also been created. "Host-only" is a virtual adapter with which the virtual machines from VirtualBox can communicate.
