The default way to access an new EC2 instance is by using your key-pair.
How can I allow other users to connect to my instance, without giving them my keys? (Ideally, I'd like them to be prompted for user/password on login)
Try the following steps:
Step 1: Edit /etc/ssh/sshd_config and set passwordAuthentication to yes.
Step 2: Run the following command:
sudo /etc/init.d/sshd reload
Step 3: Create a user:
Step 4:Set a password: