I learnt that Bitcoins and some other coins use POW, so they have transaction and mining on a same line.
That means, if all BitCoin blocks are mined in several years, does BitCoin lose its usage as transaction?
Is that right?
Also can anyone recommend me a good site where I can learn about types of cryptocurrency proofs?
PoW has two roles now.
The most important is to securely confirm the transactions.
Another role is in the fair distribution of the coin.
For the job of confirming transactions, the miners get paid. That's why each transaction needs a tx fee. It's the money for the miners.
Today the miners also get the block reward. This is decreasing and in a number of years it'll become 0. But it will not mean the world (of Bitcoin) ends. The tx fees will still be there and we all hope the price of Bitcoin and the number of transactions will make the mining still be profitable without the block reward.
For reading I recommend you start with Bitcoin wiki
https://en.bitcoin.it/wiki/Proof_of_work and Andreas Antonopoulos's "Mastering Bitcoin"
https://github.com/bitcoinbook/bitcoinbook