In order to add a Template or Campaign to an email, open up a new Compose window. You will see your Templates and Campaigns on the right hand side. The "Categories" drop down act as folders for your messaging, so click the drop down to access the correct category.
To add a template, click on Template and select the template you would like to send. If adding a campaign, you will want to click the Campaign tab instead.
If you just added/edited your messaging in toutapp.com, make sure to click the "Refresh" button to ensure that you are pulling in the most recent version.