Your hostname will be the Public DNS of your instance. it looks something like:
ec2-107-20-192-98.compute-1.amazonaws.com
Your user name will be:
- for ubuntu instance: ubuntu
- for Amazon Linux instance and the majority of the other instances: ec2-user
- for instances where ec2-user and ubuntu don't work: root
As for the password, you will have to set one using passwd command.