Do you have a kml file that you want to map in QGIS? Perhaps you found it online, or you made it in Google MyMaps or maybe you got it from Google Earth. No matter what, it's very easy to just drag and drop it into QGIS and then style it however you want.
This is the kml file I use in the video: https://tfl.gov.uk/tfl/syndication/fe...
See my intro and intermediate QGIS courses for more: https://www.udemy.com/user/alasdair-r...