The coinbase is the payment miners pay to themselves. It consists of the block reward and the transaction fees of the BTC transactions the miner includes in the block.

The block reward consists of newly created BTC. This is where all BTC comes from. It is the incentive for miners to participate and secure the Bitcoin blockchain.

All BTC comes from Bitcoin mining.

Every 4 years the block reward is cut in half. This means BTC's inflation rate is cut in half every 4 years. Eventually BTC will have no inflation around the year 2140. Bitcoin will eventually become infinitely hard money.