A single member LLC is normally a "disregarded entity" and he would report his income and expenses on a schedule C like most other self-employed persons, independent contractors and so on. (He does have a choice of filing a form to be treated as a corporation and file a corporate return, but that is beyond my ability to answer.)
https://www.irs.gov/businesses/small-businesses-self-employed/single-member-limited-liability-compan...
So as a disregarded entity, he files a schedule C. This is a form that calculates his business income, expenses, and net income. He pays self-employment tax on the net income, this is the self-employed version of social security and medicare tax. The net income also goes over to his personal tax return where it is added to any other income (stocks and bonds, spouse's income, W-2 side job, etc.) and is subject to personal deductions like mortgage interest, property taxes and charity deductions. Then he pays income tax on the final amount.
He is required to make quarterly estimated tax payments. Depending on his total income and deductions (plus your income if you work and plan to file jointly) then the estimated payments will be 15% for self-employment tax and 15%-25% of income tax, both on the net income (after expenses). Due dates are
April 15 for income from Jan-March
June 15 for income from Apr-May
Sept 15 for income from June-Aug
Jan 15 for income from Sept-Dec. (they are not all 3 months each)
Payments can be made on the IRS web site, be sure to indicate that the payments are for a 2016 form 1040ES (estimated tax) https://www.irs.gov/payments
Turbotax is not very helpful at calculating estimated payments but if you were to use Quickbooks or Quickbooks Self-Employment edition to track his income and expenses (mileage, gas, repairs, meals, out of town lodging, etc.) then Quickbooks has a calculator for estimated payments. I believe there is a web-based version so he could enter expenses on the road and not be tied to a home computer.
He needs to keep very good records of miles and expenses. And there are special rules for over the road truckers that I don't know. Someone else may be able to help.
