Operating-system review
Learn what the tool proves, not only the command name.
Operating-system questions are easier when each command or utility is connected to an observation. A network configuration tool can show addresses and gateways, but it does not prove a remote application is healthy. A process viewer can reveal resource use, but it does not by itself establish why the process is consuming resources. Event and crash data can narrow a failure, but interpretation still depends on timing and recent changes.
Use a small lab to practice ordinary administrative tasks with the minimum necessary privilege. Create users, inspect permissions, view network configuration, manage services, examine storage usage, install and remove approved applications, review logs, and test recovery options. The goal is to recognize the safest supported path for a task rather than memorize where one settings page happens to be in a particular release.
Keep file systems and data protection in the same mental model. Before resetting, reinstalling, repartitioning, or deleting, ask what user data exists, where it is backed up, whether encryption or recovery keys matter, and what organizational management state must be restored afterward. A technically successful reinstall is still a failed support outcome if it destroys the only copy of needed data.
For cross-platform work, learn durable concepts first: files, processes, services, users, groups, permissions, storage, networking, logging, updates, software installation, and recovery. Then map each concept to the supported tools on Windows, macOS, Linux, and mobile platforms.