Hope this helps ....
When working on an AWS Elastic Beanstalk instance, you can log into the system using Secure Shell (SSH), with a key pair. For EBeanstalk, that key pair was either created or selected from existing keys at the time that you created the server.
From there you have a typical TTY session with a shell on a unix-like system of some sort. (unless you picked a Windows OS, in which case I can't help you)
It's been so long since I worked on an AWS instance outside of EBeanstalk that I can't quite remember if the process is the same.