All of the answers to your question can be found here. So I think it would be better to just give you some good resources for you to have something to read in case you want to have clarification about a particular concept.
[1] https://www.lopp.net/bitcoin-information.html
[2] https://en.bitcoin.it/wiki/Main_Page

It depends on what fiat currency you will be using. Some people prefer using P2P platform for exchanging their cryptocurrencies back to fiat currency and vice versa while other people just prefer using cash app who supports cryptocurrency. This is just a general idea in terms of exchanging currencies since there are lots of ways available unless otherwise your country is not being cryptocurrency friendly.

Here are some examples for P2P Trading Platform
[2] https://hodlhodl.com/
[3] https://bisq.network/

Yes. Cryptocurrency is significantly volatile than that of traditional currencies that is why it imposes a higher risk for people who doesn't know what they are doing and has a poor risk management in terms of trading.

There are lots of risk, however, if you are planning to start getting into crypto then at least knowing how you can safely store your bitcoin or any other coin can greatly minimize the risk involved.
[4] https://notyourkeys.org/