Where you are right now may help you answer some of the questions you have. It is great if you can get on these forums with your phone and post some photos as well so we can give very specific advice.
I'm not sure of any YouTube channels which really walk people through the basics. But, you can get your questions answered here. I will give some slightly different definitions for your consideration as well.
A zone is a separate space where audio will be played. So, you already named some different areas with speakers. Multiple rooms (what are they) and outside.
I have tons of zones in my home including:
Family room (surround)
Living room
Kitchen
Outside
Dining Room
Garage
(etc., etc., etc.)
Each of these rooms is an individual space which can play different audio, at a different volume level as I choose. So, lots of zones of audio.
A channel is, as said before, a single unit of amplification. In surround sound, you might have 7 speakers, plus a subwoofer. So, you would need 7 amplifiers to power those 7 speakers. Typically all 7 amplifiers are put together into a single unit called an AV receiver that has power for all those speakers. Some rooms have more speakers, some have less. So, each speaker that receives individual audio, needs it's own power. That power will be a 'channel' of amplification.
In distributed audio, like throughout your home, you have rooms that will typically have 2 speakers in them (maybe 4). Each speaker will need it's own power as well. So, they get a 'channel' of amplification. Since most rooms have 2 speakers setup for stereo, then most rooms will require 2-channels of amplification. They are 2-channel rooms, or stereo. If a room is stereo, but has 4 speakers in it, then those four speakers will be grouped into 2-pairs of 2 speakers. That means that it still only needs 2-channels of amplification to power those speakers. If you have 6 rooms of stereo speakers in them, then that is 12 separate speakers that need amplification. If you have all six rooms as separate areas (zones) that can play different music, at different volume levels, then you need 12 channels of amplification. Yes, they sell 12-channel audio amplifiers. But, you can also group those 6 rooms together so that they play the same audio source. That means instead of 6 separate zones, you now have one single zone. You can still adjust volume differently in those rooms, but they will all play the exact same audio source. Needless to say, this is much less money to implement because you only need a 2-channel audio amplifier to make it work plus a bit of additional hardware.
For the full on 6 zone system (6 separate rooms), you need something to adjust volume in all the rooms, pick a source for all the rooms, and to amplify all the rooms separately. This is typically more flexible, but also more expensive.
www.htd.com sells whole-house audio systems and is a good place to look at for some idea of whole-house audio pricing.
