Digital coins can be used to pay for the goods and services of those who accept them. They can be exchanged for traditional currencies through the special exchange.
Issued by: System users who use computation capacities of their equipment for maintenance of the system operation (mining). Emission is decentralized and limited by the volume and time, the final volume is algorithmically limited by 21 million.
Bitcoin price dynamics is based on the confidence in it, it is formed solely by the supply/demand balance. The system doesn’t have a central body which could control the emission, influence the rate and accept or make others accept payments in Bitcoin. That’s why actual value of Bitcoin depends on the dynamics of the global volume of goods and services which one can buy for it.