When you create a form as usual by going to « Administration => Forms », you can enable the matching of a form by page URL, page path or page search query. To track a form from a certain page, click the checkbox « Track interactions in this form for forms found on specific pages, as configured below (not recommended) ». Then only specify page criteria (step 2) in « Track interactions in this form only for forms found on any of these pages (optional) ».

Previous FAQ: Is it complicated to setup the tracking of online forms?