You take the train to Ostend. Please consult the website of the N.M.B.S. (Belgian railways) for further information on departures/arrivals.
>>> Website of the Belgian railways
At Ostend Railway Station, please take bus nr. 6 “Raversijde via Luchthaven” on platform 3 which will take you straight to the airport (distance : +/- 15 minutes). There is a bus to/from the airport every 10 minutes. The bus stops just in front of the passenger building. Please contact De Lijn (Tel +32 70 220 200 (€ 0,30/min)) or consult the website of De Lijn for more information on departures/arrivals.
>>> Travel Information De Lijn