In the tree, select Database Management > FIeld Management and in the Marketo Custom Objects tab, click New Custom Object.
Enter a display name. The API Name and Plural Name populate automatically, but you can edit them. Enter a description (optional).
Slide the Show in Lead Detail to display Show if you want to ...... Click Save.
The custom object information displays. Notice that no fields, object names, or field names are linked to the custom object yet.
Editing is the same as creating, with the same fields displayed, except for the API name, which can't be edited.