In order to add a Template or Campaign to an email, open a new Compose window. Templates and Campaigns are on the right hand side. Click the Categories drop-down.
To add a template, click Template and select the template you would like to send.
If adding a campaign, click the Campaign tab instead.
If you just added/edited your messaging in the web application, make sure to click the Refresh button to ensure you're pulling in the most recent version.