To answer that in full, would be a tremendous amount of work. But let’s keep it simple: It all starts with an antennas (sometimes more than one!) and that may or may not go through an RF preamp which then may or may not go through a splitter but ultimately ends up feeding one of seven RTL-SDR USB dongles in a big USB3 hub connected to a Lenovo Tiny w/ an i7 cpu, 16GB of memory, a 250GB SSD drive, running Linux Mint as well as the infamous WebSDR software (which I cannot provide – you must speak to the author directly as it is not open source).
I’ve done many tweaks but they’re more for the advanced user so I won’t get into that here.
If you want to understand the basic concepts of SDR’s and quadrature sampling, I strongly suggest you start with Google. It is a tremendous subject and while I consider myself to be way above average (possibly expert), there are much better teachers out there. 🙂