The simple explanation I can offer is that you can do a research on You Tube (some good some misleading tutorials).
I started recording when I joined BC and since I've learnt a tiny if information.
Before you buy anything make sure your PC, laptop, I pad or whatever you use, the operating system is compatible with the audio interface.
What I did, a basic starting point.: I bought an audio interface " Focusrite Scarlett 2i2". It has two inputs. This came with a free DAW, Ableton live. Most interfaces you buy will come with a free DAW.
You plug the Focusrite Scarlett to your PC via USB, use the instructions to download package and set it up. ( It comes with a code etc).
Next step is to download your DAW to your PC/ laptop or whatever you use , then when you open the DAW you set up the preferences, audio in/out. I found the set up the most frustrating part but there are plenty of tutorial videos online.
Once it's all set up and your audio interface is connected . You plug an instrument into the interface audio and begin a new frustrating process of learning how to record etc. You will get there eventually.