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What is gas and why is it expensive at times? To understand gas, don't look to far from your everyday car. Gas paid on transactions is used to pay miners to sort and validate them. Like gas in your vehicle give it the life to run. Gas on a blockchain is essentially the blood to the the system.
Gas prices fluctuates because of how it works, each block has limited space so when traffic gets high so does price. Gas utilizes a bidding mechanism to fill blocks, the more gas paid means faster times. Each blockchain validates blocks in different times, based on network and protocol. By paying more you try to insure your transaction goes in the next block propagated, if it doesn't make it then you have to wait till the next block and hope you paid enough gas. If gas prices are to high for your taste, check back later when traffic is down and you know bidding wars for blocks aren't so intense.
Best way to check current gas prices are to use that specific blockchain's explorer.
Bitcoin: https://jochen-hoenicke.de/queue/#0,24h
Ethereum: https://etherscan.io/gastracker
