After you add an event to your Calendar, you can set to repeat it again if it's going to recur regularly.
To add an recurring event:
On your Weebly Editor page, click on the calendar.
Go to the Manage Events section.
Click on the event to edit it.
Scroll down a bit on the same page and check the Repeating event box to make your event recurring.
In the section below it, set the intervals and the end date of your repeating event.