Create a Link Field
When you create a custom object, you must provide a unique link field. A common unique ID is an email address, but for cars, the VIN (vehicle identification number) is perfect.
In the Fields tab, click New Field.
Name the link field, add an optional description, and be sure to select the Link data type.
Select whether the custom object is for a lead (person) or a company.
Select the field you want to connect the custom object to.
If you want to use the unique identifier to dedupe your list, pull the Dedupe slider over. Click Save to finish.
Click Custom Object Actions and select Publish Object to publish your your custom object.
That's it! Now, you can select your custom object in the constraints of your filters and triggers to use in your marketing programs.
You can delete a custom object, but you can't restore them, so before you click Delete Object, be sure you're truly finished with it.