What Does it Mean to "Subscribe" and/or "Follow" Someone? Why does this matter?

I'm a noob to this social media thing.  But I click on chess.com/tv and I occasionally watch the live commentating.  Very enjoyable, I might add.

Anyways, I see shout-outs by Danny Rensch and other people for "Subscribing".  Subscribing to Twitch as a matter of fact.   Why do they care about subscribers?  What does that mean exactly?   What is Twitch?  

Also, if you chat on Twitch, the commentators notice the chat.  But if you chat on Chess.com/tv, then the commentators don't notice the chat thread.  

I don't care about getting noticed by the commentators, but is it better to be on Twitch than Chess.com/tv?  What are the differences between the two?  

And what does it mean to subscribe to someone's youtube channel?

How much does someone get paid by advertisers?  Like what are rough rules of thumb (on the low or conservative guessing side) of how much a chess player could receive from advertisers?

I don't know, let me just throw out some random numbers.  Suppose someone had a 100 subscribers to their Twitch (whatever that is) or YouTube channel.  What would they get?  Or someone has like 500 subscribers, then how much would they get?  

I mean, it's like I hear them talk, and my brain translates it into, "Oh thank you, thank you, Thank you for subscribing to me and my channel.  You're such a nice person and I will praise your name on this live show for being my subscriber."  I saw one young woman who goes to Stanford and she was blowing kisses to people for watching her play online blitz against people, and then subscribing.

This must be the thing to do, I guess.

Subscribing to someone on Twitch costs 5 dollars per month. It's just another way to donate to the channel and show your support. Subscribing also has a few perks like the ability to use the channels emotes. Subscribing to someone on youtube is free. Once you subscribe on youtube any videos that channel publishes will show up in your Subscriptions feed.

$5/month for Twitch?  If I was going to do that, I'd rather obtain a paid membership on Chess.com.

Subscribing on Twitch isn't required, you can watch for free.

Can you chat on Twitch for free too?

If yes, then why does chess.com televise on both chess.com/tv and Twitch?

Yeah you can chat for free. Twitch is primarily used by people to stream video games and is hugely popular so chess.com uses Twitch so they can reach a larger audience and get more people interested in chess. They can also make money on Twitch while I don't think they can through chess.com/tv. As to why they have both Twitch and chess.com/tv  I guess it's to provide more options. Some people might be more comfortable staying on chess.com

I don't know anything about that sort of stuff either.   We dinosaurs gotta stick together.

chess.com is partners with twitch