You can connect your form to a course under Forms > (form name) > Settings. Down at the bottom there are “Sequence Settings”.
If you don’t check the “make sequence mandatory” checkbox then there will be a new checkbox and text area on the form asking if they want to join the course. You can edit this under the Content tab.
If you already have subscribers to the form another checkbox will appear asking if you want to add them to the sequence as well.