Tracking conversions with the data layer means triggering a conversion event whenever a visitor successfully completes an action that qualifies as a conversion. The data you pass in the conversion event defines the conversion.
To use the data layer on a site, the data layer module must be enabled for the site.
You can trigger conversion events from:
If you're only triggering conversion events, and not displaying any content, use shared code instead of a modification.
Figure: Tracking conversions by triggering a conversion event from shared code (click to enlarge)