How do crypto APIs work?

Could you please explain to me in simple terms how crypto APIs function? I'm interested in understanding the process by which these APIs allow developers to access and utilize blockchain data and functionalities in their applications. I'm specifically curious about how they facilitate secure and efficient data transfer, and what role they play in enabling seamless interactions between users and the cryptocurrency ecosystem. Additionally, I'm wondering if there are any common challenges or limitations associated with the use of crypto APIs that I should be aware of.