When you add/edit menu from menu operations, you see Action dropdown list. Here depending on your selection, the created menu act with the logic of the selected action definition. As you select an action from the dropdown list, the parameters for this action will be active, and you are going to fill these parameters.
If a Web Link Action is defined then the Target attribute must be left blank
Actions in Display Editors
Display editors are one of the properties of the data fields. With action concept, you would define how display editor should behave with the end user interaction.
Here you select an action type from the dropdown list, depending on your selection the properties panel refresh with the corresponding parameters.