Under what circumstances would you recommend DynamoDB over MongoDB?
If there is the expectation that the service requiring a database will scale exponentially or should be able to scale exponentially, DynamoDB offers enterprise level support and infrastructure that you can take advantage of.
Explain to a non-technical friend how DynamoDB works.
DynamoDB is a serverless database that is available for applications that need scalability and speed. Specifically, this DB provides read capabilities at speeds equaling to 1 response per second of highly accurate data. This can be increased to multiple responses per second of not as accurate data.