How does a Workflow Rule get triggered
There are four ways a Rule gets triggered:
Create: Executes the rule when records are created.
Edit: Executes the rule when existing record are modified.
Create or Edit: Executes the rule when records are created or existing records are modified.
Field Update: Executes the rule when the values of the specified fields are modified in a record.
Delete: Executes the rule when certain records are deleted.