When highlighting a resource on the Instances page, you will see next to its Public and Private IP addresses.
Clicking the button next to the Public IP will open up your default SSH client and attempt to connect to the instance. You can use the button next to the Private IP if you are connecting to the instance through a VPN or if you are on its LAN.
You can create an SSH config file named ~/.ssh/config to keep usernames in order when connecting to different hosts. In this file, these two relevant directives are Host and User.
An example of this is if you SSH into machines at work with one username and personal machines with another. Your setup could resemble the following:
# Set a global default of ec2-user (or ‘ubuntu’ or anything else you like). User ec2-user # Set the username for all hosts in the work.com zone Host *.work.com User bobcat # Set the username for all hosts in the personalstuff.com zone Host *.personalstuff.net User tiger