Every block has exactly one "coinbase transaction", the one transaction which doesn't have actual inputs, but gets all the fees and mining subsidy.
Every 210000 blocks, this subsidy halves. Right now, each block is allowed (not required!) to bring 50.00000000 BTC into circulation. Very soon, this will become 25.00000000. Four years later, 12.50000000. And this will continue: 6.25, 3.125, 1.5625, and so on. There are only 8 decimals though, and at some point the subsidy will only be 0.00000001. Four years after that, it will effectively become zero. This will not happen this century, though.
This doesn't mean that there won't be any blocks produced anymore. Assuming Bitcoin is still alive, we'll still have blocks being produced every 10 minutes. Miners will just get all their income from fees, without any subsidy.