Project submission for my Web Technology class slapped together with barebones knowledge of php.
If you want to use an actual decent flashcard app, use Anki or RemNote.

The Add page just adds a new card as a row to the database table.
Review retrieves cards due today or older. The response to a card is used to calculate its next review date.
Proper flashcard apps will use sophisticated Spaced Repition algorithms like SM-2 for the next review. This uses a more basic approach.

response1 -> next-review = today + 1 day
response2 -> next-review = today + 2 days
response3 -> next-review = today + 4 days

I've written down more features I was planning on implementing in notes.md but I lost interest as the deadline got closer.