Approval signatures are only available to use in workflow templates and when signed, it allows the form to progress through the workflow columns

It's important when setting up a workflow template, that you include the correct number of approval signatures for the number of columns you wish to have

The rule of thumb is that you always need to have one less approval signature, compared to the number of workflow columns you have

e.g If you have 4 workflow columns, you will need to have 3 approval signatures within the template

Learn more about adding signature fields to the fields editor.