Here are the steps to add "Tags" to your custom object.

• Login using an account that has 'Administrator' privileges.
• Click Settings on the top-right, and select Customize Accompa from the menu.
• In the resulting page, click the desired Add New Field link (listed below the desired custom object under "Customize Fields" section).
• On the "Add New Field" page, select the Tags field type.
• In the next page, make any customizations you'd like, and then click the Save button.

A "Tags" field will then be added to your custom object.