@Yggdrasil connect to it using an ssh program like putty for windows. Just type in the IP address, then it will ask for your username (hopefully not still root) and your password (hopefully not the plain text one you're sent in the welcome email), then just run through the setup there.
But to answer your question, enter your email as it's written, @ included.
The terminal on digital oceans dashboard is more for if you can't access through another program. (Normally due to corruption, rare, but happened to me last week. Support were great, but had no idea why it happened.)