My team used Scrum, so we started each day with a brief meeting about what things we'd done and what we were working on, and basically spend the rest of the day working on it. There was a bigger weekly meeting. Mostly it's just you and the code, punctuated with asking your team members about the finer workings of an immense codebase.
From my experience, your experience varies from team to team. Some teams give their interns their own projects and are generally detached from the software engineering team. For me, I ensured to find a team that would integrate me as if I was a new-hire even if the project wasn’t as sexy or cool. The work I was responsible for was the same as the full time engineers.