[SalesForce] Workflow to trigger upon creating a new record

Using workflows and not a trigger, how does one create a rule criteria that causes the workflow to execute upon creating a new custom record ?

E.g. When I'm adding a Customer__c record i'd like the workflow to trigger an email update.

I did some googling. Is ISNEW() or ISCHANGED() the way to go for this formula?

I tried putting ISNEW() in the rule criteria and it gives me an error, "Function ISNEW () may not be used in this type of formula".

Define the Evaluation criteria as 'Evaluate the rule when a record is created'. and simply put 'true' in workflow rule criteria formula.