If you do not own or lease the vehicle you can't use the standard mileage rate. That's because the standard mileage rate includes an allowance for depreciation (wear and tear) and only the owner or lessor is allowed to claim that.
You have to use the actual expense method for this vehicle. You need to add up the total expenses for the year -- gas, oil changes, tires, insurance, other maintenance (but not depreciation). And you also need to track the miles used for work purposes and the total vehicle miles for the year (beginning and ending odometer). You deduct the percent of actual expenses based on percent of work miles driven.
TurboTax will do all these calculations for you. You need to know the number of work miles driven, the number of total miles driven or the start and end odometer, and the total of all actual costs for fuel, etc.