Before you can apply anything in the AWS you need to have a key pair that will authenticate terraform to AWS platform so when you apply.
The simple way to do this in MAC, as i am using mac is to store it inside home folder and prove the path while using it.
So, authentication has 2 parts
key : which is stored inside home folder (/home/User/)or where-ever you wish
aws config file : ~/.aws/config which stores the authentication information entered while using aws config command