Okay, I've got this now:

public ActionResult CreateBulkCommissions()
        {
            var month = DateTime.Now.ToString("MMMM");

            var newCommissions = from enrolment in db.Enrollments
                                 select new TutorCommission()
                                 {
                                     CommissionAmount = enrolment.MonthlyFee,
                                     CommissionMonth = month,  // string constant
                                     CommissionStatus = "Unpaid",
                                     Tutor = new Tutor { TutorNoID = enrolment.Tutor.TutorNoID, TutorCommissionPercentage = enrolment.Tutor.TutorCommissionPercentage }
                                 };

            List<TutorCommission> TutorComs = newCommissions.GroupBy(g => g.Tutor).Select(s => new TutorCommission
            {
                CommissionAmount = s.Sum(u => u.CommissionAmount) * s.Key.TutorCommissionPercentage,
                TutorNoID = s.Key.TutorNoID

            }).ToList;

            foreach (var newCommission in newCommissions)
            {


                db.TutorCommission.Add(newCommission);
                db.SaveChanges();
            }

            return RedirectToAction("Index");
        }

Still gettin the same error on ToList. What must I put in the loop now?