To monitor "computer" usage there are three Window's tools: Task Manager, Resource Monitor, and Process Explorer.
Task Manager and Resource Monitor are both built into Windows. Most likely you will need to download and install Process Explorer via Microsoft's website.
I used "computer" in quotes because overall the three tools provide a great deal of information about hardware and software. What is being launched at startup, what is running, what resources are being used, and to what extent.
lt is a matter of familiarization to a great degree. Run one tool or another and observe what your system is doing while sitting idle, doing light work/browsing, watching online videos, and lastly gaming.
You do have to leave the tool window open and slid to one side of the monitor. Or use a second monitor perhaps.
The key is too not immediately react to any particular parameter or situation,. Understand what is being presented both in part and in whole ( i.e., the big picture).
And sometimes the values can skewed for one reason or another. Or a minor difference can be meaningful while a larger difference could be just circumstance.
So first look, watch, learn. Then if you determine that things are not as expected or as they should be you investigate/research accordingly.
Do not just make changes for the sake of change. Know what you are changing, why you are changing it, and what outcome you expect. Be ready to undo the change if things do not work out.
Change only one thing at a time, keep notes, and as always be sure that you have data backups (verified recoverable and readable) and a recovery disk.