If I didn't earn income or wages for 2018 only have W2-G for gambling winnings under $5,000, Do I put zero deductions or use the itemized deduction amount?

You probably don't need to file a return. The IRS has a great interactive tool that can help you determine if you need to file. Click the Begin button. It will take about 12 minutes of your time.

https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return