you will need to tell us the php query and provide us with the db table to determine the error
it looks like you're trying to post to a variable "Mary" but maybe the field should be user or name or something and the value should be mary?
you don't ask php to do that for.
It's a setting in the database table to auto-increment the records by 1
make sure the field is set as int then check the box that says auto-increment.