Apple provides applications that tell you just about everything needed to know what’s going on with your computer. I typically will use one, or all, at some point when dealing with computer problems.
The System Information Application is a great source of information about an Apple computer. you can find it in the Applications:Utilities folder (inside the Utilities Folder in the Applications folder).
The Activity Monitor Application (also in the Utilities folder: Keyboard Shortcut ⇧⌘U) is another tool provided with macOS to aid in understanding what is going on within a computer.
The Console Application (yes, also in the Utilities folder) provides access to the computers log files. Logs are records of activity for the various processes involved within the macOS. To get the most out of Console it should be run from within an Administrator account. While not the best practice, most Mac users are set up with Administrator accounts.
EtreCheck is a wonderful tool that makes diagnosing typical Mac Operating System issues as simple as can be. EtreCheck is available from the App Store or online at their own website.