Thank you for your replies.
And the complexity and hardware requirements for validating transactions is the same than the required for mining?
Mining IS validating transactions.
The process that people like to call "mining" is the process of validating transactions, building a block for the blockchain that contains those transactions, completing a proof-of-work on that block, and broadcasting that completed block to the network.
In exchange for providing this service, the Bitcoin protocol allows the entity (miner or pool) that creates that block to include a special transaction in that block which pays themselves a block reward.
That block reward consists of an inflationary block subsidy PLUS the sum of all the transaction fees of all the transactions that are included in that block.
In the beginning, that subsidy was 50 brand new bitcoins, and the transaction fees were practically zero.
As time passes (approximately every 4 years), the block subsidy is cut in half reducing the number of new bitcoins that are created. At this time the subsidy is 6.25 BTC per block. Eventually, in approximately 120 years from now, that subsidy will shrink to zero and no new bitcoins will ever again be created.
In the meantime, as bitcoin gains popularity, the number of transactions and the size of the transaction fees increases. A larger and larger percentage of the block reward comes from the transaction fees instead of the subsidy.
Eventually, the sum of the transaction fees from the transactions in the block will be greater than the subsidy portion of the reward. Then when the subsidy shrinks to zero, the fees will be 100% of the reward.
This process is what people call "mining". Perhaps as the transaction fees grow beyond 50% of the reward, people will stop calling it "mining" and instead will start calling it "transaction processing". Or, perhaps we'll ALWAYS call it "mining", and it will continue to confuse people hundreds of years from now.