The closest train station is Etterbeek. Connecting the main airport (Brussels Airport - Zaventem) with Etterbeek station, there are two direct trains per hour (direction Dinant and direction Charleroi-Sud), and the train ride takes only 25 minutes. You can look up train times and buy your tickets online here.
The closest metro station is Pétillon, the closest bus stop is Etterbeek Station / Etterbeek Gare, and the closest tram stop is VUB. The best way to check out metro, bus and tram routes, is by using Google Maps. You can even use Google Maps to navigate the campus.