GoCardless allows you to take recurring donations by direct debit - this is an overview of how it works
You add a Web Widget to a page on your web site which allows people to sign up to make a regular donation - the recurring donation appears as a recurring payment instruction on the constituent's timeline - see this for more information
Donorfy asks GoCardless to collect the donations when they become due - they then appear on the constituent's timeline
These are the things you need to do