On this page you see two buttons, that switch lists of templates for message loop and event code. List have a context menu with actions you can done with items.
New - creates new template
Edit - edit currently selected template. Editor also opens when double click on existing template.
Delete - delete currently selected template
Duplicate - create a copy of selected template
Toggle default - set "Default" flag for selected template. Flagged template will be used for generating code by pressing F9 (standard mode). Only one template in group can have this flag.
More information about code templates you can see here.