you are correct
If I need to display the error then i need to write the code only under guardcondition tag right?
Workflow Action Base is just to peform the designed action but not to validate or to throw error on screen
yes,workflow action is not designed to do validation, guard condition can do it.
besides , I believe our validation framework also supports some workflow validation.
please refer Agile Product Lifecycle Mangement for Process Extensibility Pack v3.7, section Validation Framework.