Once you have made a template, you can use it in any campaign.
Go to Marketing in the left hand menu -> Click Email Templates
Under My Templates, click New
Fill in the title of your template ie 'Team member holiday notification'
Fill in the description of your template ie 'Message to send clients to let them know about upcoming team holiday'
Fill in the subject line of your email
Click Edit email and use the email builder to design your email. You can see a full video on how to use the email builder here