When people make transactions on the Bitcoin network, they are charged a transaction fee called mining fee which goes to the miners who mine a particular block ( because the miners are using their hardware resources and also posting electricity bills ). At the beginning of any blockchain, a certain number of coins are pre-mined bruise at that point there are very few nodes on the network ( in fact any network would start with one node, then two and so on).
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From @kuldeepkaul