You can use the Event Listener tag to tell Tag Manger when you want to listen for events, and write rules for what to do next.
"Once you have your event listener set up, you can have tags fire based on form submits using a rule that looks for the event gtm.formSubmit (Of course, Tag Manager supports more than form submits: it also includes clicks and timer events.)," says product manager Lukas Bergstrom. "You can also make sure you’re getting the right form by using our Auto-Event Variable macros that let you narrow things down with attributes like the element ID and the form target."
"The end result: you can deploy event tracking to your site and send event tracking data to Google Analytics without adding any code to your site," he adds. "You can deploy measurement campaigns faster, and not writing custom code makes your solutions more robust."
Google recently launched Tag Manger for mobile apps after first showing if off at Google I/O.