"Plans" is where you find access to the plans, and the groups, lessons, and study content under a plan.
A "Plan" is like a private course you can populate with courses, groups, lessons, study content, and individual study items. Plans are created or populated via "Add to plan" links found on many pages.
The "Study" page displays the current tool, which is a mechanism for studying a study list, with options for selecting other tools and configuring the tool.
Current tools include the "Flash" tool simulating flash cards, the "Matching" tool for matching study list item translations, the "Test" tool for testing your knowledge of a study list, and the "Hands Free" tool, which lets you study or review a study list a study item at a time, without requiring interaction unless specified.