Bitcoin mining is a process of finding new blocks for bitcoin blockchain (connected list of blocks). When you find new block you discover some amount of new bitcoin coins and can confirm bitcoin network transactions.
Computers and special mining hardware around the world ‘mine’ bitcoins and competing with each other for new blocks.
Bitcoin block is a list of money transactions for some period of time. Main mining task is confirmation for validity of those transactions.
Bitcoin blockchain is a repository for all bitcoin network transactions and each participant of bitcon network can keep full copy of blockchain.
Process of mining backed by strong cryptography and special math algorithms, so bitcoin protected from any sort of falsification and invalid transactions.
If you tried to create fake or invalid transaction by altering a block that had already been in the blockchain anyone find that block is different from the one already stored in the blockchain, so our fake block will be rejected by bitcoin network.
If you do not want buy any mining hardware you can invest your money for profit from bicoin cloud mining.
Bitcoin mining for profit is very competitive process and fluctuation of bitcoin price makes it very hard to predict possible gains without speculation on the bitcoin price.