Bitcoin mining means

The process of bitcoin mining is not free, as the process of solving crypto-puzzles consumes power and requires cooling. For the currency to be viable, the miners need to be compensated for their efforts. Bitcoin miners are compensated through two mechanisms: they collect the transaction fees from the transactions recorded in the new block they contributed to the block chain, and they also collect a lump sum fee. This lump sum fee creates new Bitcoins, according to a time-varying formula. Hence, “mining” is similar to digging for gold — every now and then, a miner is rewarded with a nugget. The difficulty of crypto-puzzles are automatically adjusted such that a new block is added to the ledger approximately every 10 minutes, which ensures a predictable coin generation rate for the system, which stems inflation and makes the currency supply more predictable than it would be otherwise. In order to have a better understanding you could use an online bitcoin mining guide.

The nice thing about having crypto-puzzles that are so difficult is that it is difficult for an attacker to modify the ledger. Someone who wants to, say, buy something from a Bitcoin merchant, get the goods shipped, and then later change that block, faces a very difficult task: they need to find alternative solutions to cryptopuzzles for that block and every subsequent block. What makes this difficult is that the main bulk of the miners will be working hard on adding new blocks at the tail end of the ledger, so an attacker, with limited resources, cannot hope to find alternative solutions for all the past blocks and catch up to the rest of the miners.

Miners today organize themselves into groups known as pools. A pool will typically consist of a set of cooperating nodes that share their revenues whenever they find blocks. Mining pools are kind of like the shared tip jar at a restaurant: on occasion, a miner will hit the potluck, discover a good solution to a cryptopuzzle, and rake in some revenues, kind of like a waiter who lands a big table that runs a large tab. Since this occurs relatively infrequently from the point of view of any given miner, sharing the proceeds enables the miners to have more predictability in their lives.