Arriving and driving through Freising might not be considered the most joyful experience. Streets are narrow, crowded (on work days) and often one-way. Free parking space is rare. Thats what you get when you place a town between two hills and two rivers.
There is a small "short-time" parking lot near the train station. Maybe a good first stop for orientation. If you want to visit the city center use the parking garage "Am Wörth". There is also a big and free parking lot across the railroad tracks at "Luitpold Strasse" called "P+R" that is "Park + Ride", because you can park your car there and ride to Munich by train. Its in walking distance to city center, but quite difficult to reach by car.
Freising can be reached by the S-bahn (Line S1) from Munich. Therefore this is a very convenient way of getting to Freising. You will be put within walking distance to the city center when you arrive at the station.