Additional workflows can only be added to a page/form. This is because only pages/forms have more than one event associated with it that can trigger a workflow.
Workflows for buttons, for example, can only be triggered when a user clicks on it. A form, however, can trigger a workflow when the form loads, when a user saves the form, when a save attempt fails, etc.
To integrate multiple workflows to a single page or form, follow the same steps outlined in Creating a Workflow.