When you switch to Campaigns from the project, you will see the main view
and the Template Chooser is already opened.
Campaigns with Template Chooser
Otherwise, you have to click the + button to open the Template Chooser.
Campaigns with Create Campaign Button
Now, select the template you want to use for your campaign. A template defines
the channels and slots for your campaign. When you hover over a template entry,
you will see the supported channels.
Click the Use Template button to select the template.