From Ben-Gurion Airport to Tel-Aviv, the Sheraton Moriah hotel:
The best way is by taxi. Follow the signs to the taxi dispatching area. There is a fixed price of about 100 shekels (~20 USD) to anywhere in Tel-Aviv. It is a ~20-35 min ride, depending on traffic.
From Sheraton Moriah to the Tel-Aviv University Campus:
A shuttle bus will leave the hotel every morning at 9:00 AM, and will take the participants to the University. In case you choose to come on your own, again, the best way is by taxi (have the hotel call a taxi, or flag down one on the street). It is a 10-15 min ride, costing about 25 shekel (~5 USD), according to the meter. (You should insist that the driver operate the meter.) Ask the driver to be taken to Tel-Aviv University, and to enter through gate 4 (Ramniceanu), on George Wise St. (formerly Klausner St.; see campus map). Get off in the parking lot next to a red marble building with a superstructure consisting of two huge cylinders (the Cymbalista Jewish Heritage Center). There will be steps on your right leading up to the Physics Building (Shenkar), which has written on its facade: "The Faculty of Exact Sciences".