How to Access the Prompt Box to Enter Context Files and Visual Content After Opening a New Project

I opened a new project the other day and didn't enter a prompt, and then closed the project. Today I came back, and I can't figure out how to get to that prompt box again, where I can enter all my context files and visual content. And it just offers me to "generate a brief". I thought that might be it, but it just generated a meaningless brief for me. I'm trying to get to work and I can't figure out where to start!