To create professional looking emails to send to your customers, first make sure you have access to Campaigns by clicking Apps and Integrations > App store > toggling on Email & SMS Marketing Suite.
Drag and drop templates can be used with the following Marketing features: Sequences, One-off messages, and Marketing Templates.
If you know you'll be leveraging the same images and text in many different future messages to your customer base, you'll save the most time by creating your Marketing templates first, then loading these templates later on in Sequences and One-off messages. After loading the template, you can make changes to the text, images or format.
Once you've pulled up a drag and drop form, before adding any content you may want to consider using Blocks. These divide the email into sections that can help you achieve the desired outcome.
Once you're happy with the layout, use the Content tab to start dragging items in.
Use the Body tab to edit text styles / colors / weights as well as background color.
Note that you'll have the option auto-save your work using the checkbox at the bottom.
Remember to start creating in Marketing Templates for easy access later on, using the load from template option.