How do you buy USD?

Excuse me, I'm curious about the process of acquiring US dollars. Could you elaborate on the steps involved? Specifically, what methods do individuals typically use to buy USD? Is it through a bank, an exchange service, or some other channel? Additionally, are there any specific requirements or documentation needed for the transaction? I'm also interested in knowing if there are any potential risks or fees associated with buying USD, and how to minimize them. Thank you for your time and assistance in clarifying this matter.