I need to create a formula field on createddate of user object to parse the month and year from it .But this field is not visible in formula merge options.But this field is visible on reports ....How to get my formula done on created date??
Unfortunately you can't do this. I can't find any documentation from Salesforce on this, but there's an existing answer on success.salesforce.com:
It isn't available in the workflow formula editor either, so it looks like your only option is a regular field and a trigger to update the value whenever a record is created/updated.