How much is a dollar in OKX?

Excuse me, I was wondering if you could help me understand something about the OKX platform. I'm curious about the value of a dollar when converted into the currency or token used on OKX. Is there a fixed exchange rate, or does it fluctuate based on market conditions? I'm trying to get a clear picture of how much I would need to invest in order to purchase a certain amount of cryptocurrency on the platform. Can you provide me with some guidance or insight into this matter?