First of all, please bear in mind that HKUST is one of the eight universities in Hong Kong. Two older and better-known ones are Hong Kong University (HKU) and Chinese University of Hong Kong (CUHK). If you ask directions to HKUST in the city, you might want to tell people that you are going to the university in Clear Water Bay (in Chinese characters: ) near Sai Kung, even though HKUST is officially in the district of Kowloon (). The Chinese name of HKUST is written as .
Second, HKUST is a little bit remote (see a map of HKUST's location) by Hong Kong's standard, because it is by the sea, on the hills, and not directly reachable by MTR (Massive Transit Railway, the public subway transportation)! The nearest MTR stations to HKUST are Hang Hau (to the south of HKUST, exit B1) and Choi Hung (to the west of HKUST, exit C1). You can then take mini-buses (11,11M or 11S, all having signs showing "HKUST" as the destination) from these MTR stations. The bus ride takes about 10-15 minutes. Alternatively, you can take a taxi to HKUST from any point in the city. A taxi ride from the Hong Kong airport to HKUST goes all the way east, takes about 40 minutes, and costs around HK$350 (US$45). Other trips from some place around Hong Kong to HKUST are typically much shorter than the airport ride.
Third, you don't need to worry about which building to go to in HKUST - there is only one huge, octpus-like academic building on the campus. If you see the main gate of HKUST after stepping off a bus or a taxi, walk about a hundred meters down the hill, and you will be in the university piazza with a red sundial structure in the center. The academic building is right in front of you.
Fourth, the CSE Department is on the third floor of the academic building, near Lifts (Elevators) No. 25-26. When you walk into the atrium (the lobby space with seven-floor high glass ceiling) of the academic building, you will see stairs and escalators on the right. Take the escalator up and you will be in the academic concourse. Walk along this concourse by about another one hundred meters, you will see a little coffee shop with tables and chairs outside. Turn left before you run into the coffee stand and you will see Lifts 25-26 on your right. Ride either elevator to the third floor, step out of the elevator, and go through the door on your right. You will see the Office of the CS Department (and a photoboard of the CS faculty) across the hallway. The administrative staff in the office will be happy to get you your host.
Enjoy your visit at the CSE Department, at HKUST, and in Hong Kong!