After you have seen this HowTo video and read this article you will know how to create an action which triggers on a scheduled moment, as every week on Monday at 09 o'clock in the morning.
Go to Actions
Create a Scheduled action
Generate the cronjob you want*
Create a loop event
Create a collection of users to loop through
Create a Send Mail event
Fill the fields necessary for you Send Mail event
Create a mail template
*cronjob is a notation used to define certain moments when you execute an certain action. You can use this link to generate the cronjob you need.