Yes, confirming that the X9 is the express.
Click on the second link that OverThereTooMuch has posted, then, on that page, click on the third link from the top (site plan Tegel airport).
On that map, find the yellow cube at the edge of Terminal A that says "BVG" (that is the name of the Berlin transit system).
The cube is the ticket window, you buy your ticket there. Once you have your ticket exit to the outside and find the stop for the X9 (same map, X9 stop is the purple rectangle).
When buying your ticket, you can buy a single journey for €2,70 or an all-day ticket for €7,00. The all-day ticket is good for all busses, U-Bahn and S-Bahn trains and for all trams (only the separate town of Potsdam is excluded).
Last edited by Non-NonRev; Jul 16, 2016 at 6:31 pm