MIDI channels, confused

Hi! It's my first day here - or second, counting the sleep - and I must say the forum is quite overwhelming, as is REAPER itself, with the many many options and details and things I don't know anything about yet. I still can't get my head around "MIDI channels". What I do know is, that a MIDI-signal has 16 MIDI channels, each of which can be seperately "programmed". Does this mean that, in theory, I could record a max of 16 different instruments at once? I'm planning on doing that, just trying to understand how it works. What confuses me, is the "map input to channel"-option, where does this send the input to, exactly, if it even sends something? When setting the input of a track, I can choose from the MIDI router, Reaper's virtual keyboard and "all channels" - all of them have 16 channels. For the router and the virtual keyboard I understand that, but what does "all channels" refer to? The MIDI-out channels from the track itself? But then when I map track 1's input to channel 2, shouldn't I be able to receive that input by setting the input of track 2 to channel 2? And then there's the option to change the number of channels for a track and the CC's and the "OUT"-signals from the VSTi's.. I can't draw an image in my mind of how things would be "wired up". I'm trying to find out by changing settings and observing the changes, but this is not very satisfying. I searched for explanations and did find a lot of info, but somehow it doesn't "fit together" in my mind. A visual explanation, like a picture of channels and what they "contain", where they are (in the abstract sense, I know you can't touch or eat them ;)), etc. would be very nice, but I haven't been able to find that yet. Maybe somebody here can explain it to me, or knows some pages where this is explained more "visually"? Regards and sorry for the mess.

There are some really nice video tutorials . And Groove3 has a comprehensive video tutorial. See how to get 30-day free all-access.

Nice, thanks! First link I had already found, Groove3 I hadn't bumped into yet, excellent.