In order to understand why your internet is slow, fast or in between, consider the connection to your house as being a hosepipe.
If you have an old style copper adsl connection, this can be likened to a very small hose pipe (small diameter), no matter how wide you turn the tap on, you will only get a gentle flow of water. If you connected a number of taps to this pipe and turned them all on at once, each tap would only produce a trickle. This is the same with your devices, when using only one device on an adsl connection you may struggle to watch Netflix but could send emails and browse facebook. If a few people in the same house tried to watch Netflix, play online games or attend a Zoom call, they would experience buffering and most likely completely drop off.
If you have a fibre optic internet connection, this can be likened to a large hose (big diameter) this now allows multiple taps to be turned on simultaneously and all provide strong consistent pressure as it would be with your devices, multiple users in the home could stream video content, play online games, stream music and more without buffering or drop offs.
That being said, a fibre optic connection is also limited by the speed determined by the internet provider, a lot of users are on the 100/20 plan which is no longer fast enough for our needs. If this is the case at your place, call your provider and get upgraded to fibremax, this has a maximum speed of 900mbs, this is a big hose pipe with the tap wide open.
If you live rurally the biggest pipe you can get is a rural broadband or a satellite connection, they are still small hoses providing a maximum speed of around 40mbs but unfortunately your only option until fibre arrives.
For information on how to test your internet speed, click here.