The Google Tag Manager data layer is an object that contains all of the information that people want to pass to Google Tag Manager from their website.

Information, such as events or variables, can be passed to Google Tag Manager via the data layer, and triggers can be set up in Google Tag Manager based on the values of variables or based on the specific events.

Variable values can also be passed through to other tags (for example, pass purchase total into the value field of a tag).

Step 1: Define the data layer in your HTML; see following example:

<script>dataLayer = [{'content_ids': ['123']'total' : '300'}];</script><!-- Google Tag Manager-->...<!-- End Google Tag Manager -->

Step 2: In GTM define the data layer variable at Variables → User-Defined Variables.

Step 3: In tag HTML, you can reference the data layer by the {{ }} placeholder; for example:

fbq('track', 'Purchase', {content_ids: {{content_ids}},content_type: 'product', value: {{total}}}];