Yup, rack on the roof. Not a must, but totally worth it if you will be carrying a board a lot, or have a reasonably shiny car.
If you have rails, you put bars across them, if you have gutters, then you buy a rack that goes in those etc. Decent rack systems have dedicated feet for different models, and the bars attach to those.
Have a look at
www.thule.com you can search for the kits by car model. Thule are at the top end of the price range, but IMO well worth it because the racks last forever, and if you change your car, you can usually just swap out the foot pack to fit the new one. If you get locking racks, you can get a few different solutions for locking your board to the racks too, which is worth it for peace of mind sometimes.
Then just get some webbing tie downs to strap the board to the racks.