Marking topics in Firecracker tells our system that you've learned that material, thus unlocking the questions we have associated with those topics you've marked. You can mark topics via the Today's To-Do's page, as well as via our Study Something Specific page, both on mobile and on the web. To mark topics in bulk, go to Study Something Specific and choose the "Manage Marks" button.
The topics that you mark will compose your recommendations "To-Do" in Firecracker. Your Today's To-Do's recommendations automatically refresh at the start of each new day. You can adjust when your "Day Starts At" via the Account and Settings page. Here's a guide on best practices for marking topics: http://blog.firecracker.me/students/best-practices-for-marking-on-firecracker