There are a few options to get from the Ben Gurion airport (TLV) to Jerusalem:
485 bus service: Depart every hour on the hour (xx:00), 6 days a week – not during Shabat and Jewish holidays. Last bus on Friday is at 14:00 and first one on Saturday is 21:00. The bus stop is located outside at the 2nd floor signposted “Public transport”.
The bus is white with green logo (pic).
Schedule: Ben Gurion -> Jerusalem, Jerusalem -> Ben Gurion. Price is 16 Shekels one way
Shuttle Taxi: The yellow/white 10 passengers vans outside the Arrival hall (ground floor, operated by “Nesher”) will take you from the airport to any address in Jerusalem. The downside is that you have to wait until there will be 10 passengers in the van, good chance your driver will be rude and loud, and it mighא be a long and winding drive through the streets while dropping off other passengers before you. Price is 64 Shekels one way.