Action parameters provide the information that an action needs to perform its job. Parameters may be required or optional. For example, for a Perform Loose Page Output action, the Process Template Path is a required parameter that you must supply a value for. An automation rule is not valid until all of the required action parameters are defined.
Some parameters have default values. For example, in an Email action, the Priority parameter has a default value of Normal.
Some parameters are required. For example, the Email action has a To parameter that is required and not set by default.