permission denied (publickey) - AWS EC2

I am trying to get a Django app running on Amazon EC2. I currently have my .pem file saved in the root of my Django project.

When I try this

chmod 600 oby.pem
ssh -i oby.pem ubuntu@52.0.215.90

in my mac terminal, I receive this error: Permission denied (publickey).

• To begin, am I saving the my oby.pem file in the right location? If not, where should it go?
• Furthermore, what are the necessary steps to correctly set up the ssh key?

Thank you!