Hello! Welcome to the forum!
The purpose of the media query, in this case, is to make your Technical Documentation page responsive to whichever device a user would like to view it on. The term responsive here can be a bit ambiguous since the real meaning is that the content fits properly (and is usable) equally well when view on a mobile device, tablet, or full screen desktop, etc.
There are lots of good examples to look at online like w3 schools and mdn, etc.
A good strategy to tackle the different screen sizes is to decide on the screen size you will use as your basis and then use the media query to style the other sizes by just adding amendments to your existing styles. The convention is either mobile first or desktop first and really it is up to you to decide which you are most comfortable with.
Does this help?
Keep up the good progress!
Happy Coding! 