FSMonitor is intended to track any changes that occur in your system, by listing all file modifications. The app is easy to use; however, I must alert you that technical knowledge is required to understand the results properly. In this respect, the help documentation can only help you operate the tool.
The first step you should take is to start recording events. Immediately after, the results will begin to appear in form of a tree by default. Moreover, you can switch to other views, including Text, List and Columns. Since the data is updated in real time, you can actually see how the tree grows as more changes happen. Tracking all system events at the same time is quite difficult, so it is great that the tool supports using quite complex filters, by defining given events or strings.
If you click on a particular item, it is opened on Finder, so that you can check the changes. Besides, you can also open the Inspector panel, which appears on the left side to provide you with details about the item, including modification date and related events, processes and sessions. Finally, it is also possible to export the registered data as TXT or JSON files.
To conclude, FS Monitor is not the kind of tool everybody needs to have. Actually, many users would not even know what to do with the information it provides. Yet, in expert hands, this product is essential for solving problems with the system that would otherwise be too difficult, if not impossible, to diagnose. You should know, however, that there are similar tools, some of them are available for free. Besides, at least one of them allows triggering alerts when a change to the selected item is made.