The email editor supports merge fields, that is placeholders for dynamic content that will be replaced during the rendering. This makes it very easy for editors to insert dynamic content inside the editor.
Some of the built in merge fields are:
Each "Custom Field" on a recipient can also be inserted as a merge field in the email editor.
It's possible to add custom merge fields to the email editor, this is useful if you create a custom integration and would like to append more dynamic fields that the editor can choose from so that they don't have to remember the exact name, this is done using a "Merge Field Provider.