To apply conditioner and/or oil to the hair before shampooing is a called a pre-poo treatment (pre-shampoo treatment). A pre-poo softens hair and gets all the knots, etc. out before washing. It will eliminate frizz after washing and makes detangling so much easier.
Use your favorite conditioner first, let it sit for 5 minutes or so, rinse, then apply your favorite sulfate-free shampoo.