Sign into your Google Adwords Account (https://ads.google.com) and click on the spanner/wrench in the top right of the screen - in some cases this is labelled as "Tools"
Click on "Conversions" in the "MEASUREMENT" section
Click on the conversion that you would like the ID and Label for
Expand the Tag Setup section and click on "Use Google Tag Manager", the Conversion ID and Conversion Label can be found there.
