Changing ‘nameservers’ potentially breaks your website (and email!). So it’s something to handle very carefully.
Without getting all technical, when you change nameservers for your domain name you are telling ‘the internet’ to look elsewhere to find details about where your website can be found. So typically you would update these settings if you changed web hosting company for example.
The problem is that there are 2 ‘layers’ to these domain records.
And nameservers are the top layer of this.