AWS cli wrapper, how does it know where your ec2 instances are?

I'm working with this aws cli wrapper: http://ift.tt/14vsA2G

But I can't get it to work, when I try to use "describe instances" the error code says

A client error (InvalidInstanceID.NotFound) occurred when calling the DescribeInstances
operation: The instance ID 'i-********' does not exist. 

(I added the asterisks)

Then I was thinking, it doesn't have my access key and secret key, so how would it know?

I tried setting the endpoint in my constructor too, but to no avail. Can someone tell me how this works?