How do I create a repeating to do item?
You can create a to do item that repeats daily, weekly, monthly, yearly, or by a time period you specify.

What are categories and how can I use them in To Do?
Categories are labels that help you organize items and find them more easily. You can use categories to organize calendar entries, to do items, contacts, or groups. You can assign category colors, so entries in a category appear in a different color on your calendar.