How does it work

Greetings.

I have been reading about Bitcoin on the internet, even bought a book about it, but I still can't understand how it works. Because of that I decided to go through embarrassment of asing directly to people with more knowledge and xp about it.

Some questions that I have, I hope somebody can enlight me:

1 - If the bitcoin never actually leaves the network, how can you buy or pay with it?

2 - The wallets, there are hot (online) and cold (offline), but they don't keep the bitcoins, they just keep the passfrases? If yes, how can you transfer satoshis or coins from one to another?

3 - Is the only way to have bitcoins by using wallets or can I create something in the actuall network and operate there?

4 - I understand that's not something you can use for gambling or trade, but as a reserve of value for the long run (some people even say for the entire life pass generations), but how can it be useful in the real world? If you have dolars, you can invest it and take passive income. If you have gold, it values considerably fast and is accepted everywhere, but what about bitcoin? It seems to me you buy it from a broker, stock it and never use it because it's not accepted anywhere, some people even laugh you talk about it.