Just need to place the WebBlock in your page or in layout (If you need GTM in all pages), to have this working only have to be passed Google Tag Manager ID (GTM-ID).
Also exists a client action ready made to send events full customized, you can define which variables you need and the correspondent value.
- https://developers.google.com/tag-manager/quickstart?hl=pt-br
- https://developers.google.com/tag-manager/devguide?hl=pt-br#events