There isn't a dedicated habit tracker feature in Marvin yet. But this is planned.
Please add your vote and wishes for this feature here: https://portal.productboard.com/gvwfgxmcwqylldrxlfagmgkw/c/101-habits
If you do want to add some habits to Marvin you can set them up as recurring tasks.
If you want to separate your habits from your regular task list, go to the workflow library and select the "separate habits" snippet. It lets you add a @habit label to habits which will then get filtered out into a separate list.