Its quite simply yet can seem complexed. Heres the most common signal chain used to record music:
Instrument - Microphone (if needed) - audio interface which is the bridge between the outside world and your computer and contains mic pre amps, instrument inserts, analog to digital converters - computer - digital audio workstation, such as Live, Logic or Pro tools, which is like a recording studio inside your computer. This is the recording signal chain...heres the playback signal chain once you have actually got music recorded into the computer.
Digital audio workstation - computer - audio interface where the digital signal is converted back to audio - studio monitors / headphones to hear your creation.
The audio interface as a bridge between the analog world and the digital one inside the computer is very important, the computer you use is not so important just that the operating system specs are able to communicate with your audio interface.
There is just so much info out there in the www......with lots of helpful videos.
Lastly consider your budget.....entry into the recording world is very affordable but its important to have an idea of the necessary equipment that you need and what you dont need....this usually requires experience but as I said there are plenty of places out there to help with these specifics and naturally encourage you to purchase from them
Good luck....its an amazing journey!