Any prescribed habit will simply appear on your "Things to do today" section on your Dash, or on your Calendar for the prescribed days.
In the screenshot below, you're lookin at your Calendar tab. You simply tap on the habit to open and then tap Complete when you want to mark it as done.
A winning streak (or “streak” for short) is when you complete a scheduled habit for 2 or more days in a row. To count toward a streak, a habit must be marked as completed by noon on the day after it was scheduled. You can create winning streaks for each habit assigned added to your personal calendar.
As your streak continues to grow, you will receive special badges at various milestones. When you hit a milestone, immediately after marking a habit as completed, you will see a summary screen awarding you with a badge with a special congratulatory message and information about the next milestone you're aiming for.