When creating or editing an email template, in the content tab, you have 'Title'
This will create large text that will be used as a heading for your email. To put it in to the template, simply click and drag in to the template.
Once you click on the new title block, you can then start to write your own title. As you do this, you will see a small list of options pop up which help you change things like bold, italics, underlined, colour etc.
There is also an option to select Dynamic Variables
On the right of the screen is the more advanced options for your title, which include things like title type, font, colours etc.