IAM user roles and user question

I need help understanding the IAM role you are referring to. However, the following document may help you to understand what a role can do.

https://docs.aws.amazon.com/aws-managed-policy/latest/reference/policy-list.html

What a role can do is expressed as a set of policies. And since many people use AWS Managed Policy to save time and effort, reading the description of AWS Managed Policy will help you understand.