If you are eligible to deduct vehicle expenses, you can deduct either the standard mileage rate or actual expenses, not both. The standard mileage rate covers all expenses of operating the vehicle, including gas, maintenance and repairs, insurance, depreciation, etc. So you cannot deduct both mileage and gas. It's one or the other.
How you claim the deduction depends on whether it's for a job where you get a W-2, or for your own business or self-employment. As DoninGA said, if it's for a W-2 job, the deduction has been eliminated for 2018 through 2025. If it's for your own business or self-employment, you enter it along with your other business expenses.
