So what is a Cryptocurrency? 

A cryptocurrency is a digital currency. Crypto refers to the encryption algorithms, the privacy and other functions of the currencies.

What problem does a cryptocurrency solve? 

It fixes corruption, theft, inflation, incompetence, inefficiencies, speed, privacy, intermediaries, energy, and trust.

Is cryptocurrencies better than FIAT currencies?

Yes. The cryptocurrencies are not regulated by central banks and authorities. People also don't need the approval of a bank to transfer their money. They just get the confirmation about the transcactions. With cryptocurrencies we get rid of the need of the middle-man, and we are able to control better our finances and our privacy. Blockchain technology provides security 24/7 to the users.

How fast are the crypto-transcactions?

That depends on the blockchain. The speed is calculate on TPS, Transcactions Per Seconds. Bitcoin is 7, Ethereum is 14, Cardano is 250, Solana test was up to 50000.