Dynamic Content primarily pertains to transactional email campaigns.
The Code Editor (Legacy) was formerly referred to as the "HTML Editor."
Once you choose a template that utilizes dynamic content and/or personalization tags in your campaign you must always edit the campaign in either the Studio editor or Code Editor (Legacy); you cannot change to the Drag & Drop Editor (Legacy).
View Dynamic Content in your Template
Select Continue Draft to open the HTML Editor.
Highlight Dynamic Content
Once you have created Dynamic Content, select the Highlight Dynamic Content button on the toolbar to highlight your dynamic fields within your template.
Edit Dynamic Content
Right-click on any highlighted section of Dynamic Content you wish to edit.
Make your edits in the Dynamic Element tab.