What is the Gas? WTF?

As usual I've gone to the internet... After I read several articles I've understand the following not very obvious things... 

To make transaction or execute smart contract you need to pay fee. In the real banks the calculation is very simple, for instance you need to pay 3% from the amount of the transaction. In the case of Ethereum the calculation of transaction price is more complicated.

To make transaction or execute smart contract in Ethereum you need to pay some amount of "Gas". For instance for single money transfer you need to pay 21000 Gas units. But what is the cost of one unit of gas? You must set it by yourself... The price is defined in GWEI (I didn't found what means the abbrewiation) but 1,000,000,000 GWEI = 1 ETH. So in my transaction was:

Gas Limit: 21000
Gas Price: 41 GWEI (0.000000041 ETH)

So the fee of my transaction was 21000*0.000000041 = 0.000861 ETH. Ok I've found my money! ;) But stop... In rubels it is approximately 10 RUB but the amount of the transaction was only 0,0044 RUB so I've paid  223102% !!! WTF?!!!

From my point of view it is too much... And the next Big question - can I decrease by myself the "Gas Limit" and "Gas Price" ? After interesting reading I understand that it is not recommended decrease "Gas Limit", but you can set "Gas Price". What is correct gas price? To know it you can visit Gas Station! ;) https://ethgasstation.info/ What we can see for this moment?

Recommended safe price is 5.1 GWEI. It means that if you set the price 5.1 than your transaction for sure will executed in the next 30 minutes. If you need to execute your payment less than in 2 minutes it is necessary set the Gas price equal 14 GWEI. Why default price of Gas for my transaction was 41 GWEI ?!!! It is very looks like some kind of cheating... (((  Um no cheating I found the info about default 41 GWEI... It is the price to make instant online transactions...

But I have enough time to make brave experiments with Gas!