Dragging and dropping the Title widget on top of blocks creates Title text in your email (Fig 1). 

Fig 1

To edit the Title, click on the Title widget to get access to the toolbar where you can format the Title text exactly how you like (Fig 2). 

Fig 2

To learn more about the other sections within Widgets, read the corresponding article:

• Widgets - Text
• Widgets - Image
• Widgets - Video 
• Widgets - Space
• Widgets - Divider
• Widgets - Button
• Widgets - Social Sharing
• Widgets - Icon 
• Widgets - Image + Text
• Widgets - Countdown Timer (still in development)