There are three types of reminders you may enable for medication or other treatment modalities (such as therapies, activity, etc).
They are: Daily, Weekly, Variable Days
Daily as the name implies allows you get a reminder DAILY at a set time, you may click + and add various times you want to be reminded to take a certain medication.
Weekly as the name implies allows you to get reminders on certain DAYS of the week. Clicking + allows you select a day, such as Monday, and Tuesday and then let's you select a time on that day to be reminded.
Variable Days reminders allow you to be reminded every certain amount of days. If you set variable reminders to 10:00am, 5 - This will mean you will be reminded to take a certain medication (or any modality) every 5th day. So if you enable it on a Monday, you would receive the reminder on Saturday.
You may learn more about tracking your medicine here.