Retain keeps a record of every topic you've revised, how it went, and when it's due again — so you always know where you are in a subject. No decks to build, no cards to write.
Your tag is already selected, so the list is short. Tap a topic, or add a new one right there — no setting up a subject tree first.
Today by default — or backdate a session you forgot to log. Then one honest answer: struggled, getting there, or confident. That's what sets the next date.
Week or month, filtered by tag. Coloured entries are sessions you've done; outlined ones are still to come. Tap any of them to edit how it went, or move it to another day.
Each tag fills with colour as its topics firm up — red early, green once it's holding. Open one to see every topic and every session you've logged against it.