The train station in Freiburg is Freiburg (Breisgau) Hbf. When you buy your tickets, be careful not to confuse this with Fribourg, which is in Switzerland.
If you are coming from France, there are local connections from Mulhouse (with a short change at Müllheim, see here or here, according to whether you are in France or in Germany) as well as from Strasbourg (changing in Offenburg). The fare Mulhouse-Freiburg is a special fare that you buy directly at the ticket vending machine. Besides, there are several high-speed trains Paris-Karlsruhe-Freiburg. There is a direct TGV Paris Est-Freiburg once a day (departing at 5:22pm from Paris Est and arriving in Freiburg at 8:30pm).
From Strasbourg you could also take a direct FlixBus. Take into account that the FlixBus stop in Strasbourg is not next to the central train station.
The best airports to reach Freiburg are Frankfurt (FRA) and Basel (BSL).
There is a direct bus from Basel Airport to Freiburg; alternatively, you can take a bus to Basel train station SBB and then the train.
The train ride from Frankfurt airport to Freiburg is about two hours. Several airlines (Lufthansa and partner airlines, etc.) offer the Rail&Fly option to combine your flight ticket with a train ticket. We recommed this option if you are flying to/from Frankfurt.
Note: On Saturday, November 18th there will be no high-speed train on part of the railway between Freiburg and Frankfurt due to construction work. If you are planning on flying back from Frankfurt on the 18th, make sure to plan your train journey accordingly.