2018 taxes have been filed. I itemized, turbo tax decided standard deduction was best. I did not pay any taxes but did not receive a refund either? why would that be?

In most cases when you don't have any tax withheld during the year you will not receive a refund. Most refunds are simply an overpayment of tax that was made during the year; if you didn't pay any tax in through withholding or making quarterly estimated payments it's normal to not have a refund.