How to grant EC2 access to SQS

The docs are very confusing to me. I have read through the SQS access docs. But what really throws me is this page: http://ift.tt/1fHnpSq

You can provide your credential profile like in the preceding example, specify your access keys directly (via key and secret), or you can choose to omit any credential information if you are using AWS Identity and Access Management (IAM) roles for EC2 instances or credentials sourced from the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables.

1) Regarding what I have bolded, how is that possible? I cannot find steps whereas you are able to grant EC2 instances access to SQS using IAM roles. This is very confusing.

2) Where would the aforementioned environment variables be placed? And where would you get the key and secret from?

Can someone help clarify?