Bitcoin mining is the process by which new Bitcoins are generated. When you perfom mining, your computer adds new Bitcoin transactions to the block chain (a public ledger where all Bitcoin transactions are stored) and searches for new blocks. A block is a file that has the most recent Bitcoin transactions recorded in it. When your computer discovers a new block, you receive a certain number of Bitcoins. Currently a block contains BTC 25. This number changes throughout time and gets smaller by the factor 0.5 every four years. (IN OTHER Words value is increased evvery 4 years)