My day job is a network engineer for an ISP. We actually specialise in high speed low latency fibre connectivity but we do provide all the usual ISP services such as broadband (DSL), hosting, voice, and so on.
People regularly ask me about how they can improve their broadband or steps they can take to ensure they are getting the best they can from their service providers connection (which essentially entails how it works).
I wouldn't touch too much on how it works as that can get very technical but there are lots of strait forward steps you can take to ensure you aren't hindering yourself. Such steps include;
- Checks and improvements to you last mile wiring
- Checks and improvements to your home wiring (if you use a wired Ethernet connection)
- Checks and improvements to your wireless configuration (if you use wireless at home)
- Checks you can make on your broadband quality and how to know when you have grounds to approach your ISP for help (how to know when a poor broadband experience is the fault of the ISP)