Miners choose transactions with higher transfer fees and select them to be written in a new block.
That's where the race begins
Every ~10 minutes, all miners in the world are racing to solve a mathematical problem based on asymmetric cryptography to be prized as winners and write a new block.
As a result of their effort and work employed in this process, the winner is rewarded with all the transaction fees contained in that block and newly minted bitcoins (6,25 per block).
To be more competitive and be able to have predictable results, since the odds to solve a block alone is very low, miners join mining pools where the work to solve a block is distributed through all participants of that pool.
The reward is shared proportionally to the amount of computer power applied in that share of time. This way the reward is shared with all the participants each newly mined block.
The mining pool can transfer the addressed payment daily if wanted, this way it is possible to have a steady crypto income.