Installing BrainyMetrics on WordPress takes one snippet in the site-wide head code: Appearance → Theme File Editor → header.php before </head>, or a header-scripts plugin such as WPCode (use a child theme so updates don't remove it). From then on every visit records its source, campaign and ad, and forms are captured as leads automatically.
Connect your payment processor or checkout to attribute sales, and list any other domains you use (a funnel, a booking page) so visitors are followed across them.