Most of the larger airlines (also known as the expensive airlines) travel to Brussels Airport (not Charleroi). The low-cost-carriers like WizzAir, RyanAir and Easyjet fly to Charleroi, while Lufthansa, British Airways and so on come to Brussels Airport. This airport is located only 12 kilometers from brussels making it one of the most central airports in the world. As you arrive to Brussels Airport there are several ways of getting to the city center, and here you can find some of them.
There is railway station at the airport, and the trains leave from here to several large cities in Belgium every hour. This makes it ideal for travelling to either Brussels or to other destinations in Belgium.
There are taxis waiting outside the terminal taking you to the city center for approximately 35 Euro. You should though be aware about the fact that there are unlicensed taxis waiting as well, and entering into the wrong taxi might make you have to pay more. Autolux and Unitax are two taxi companies in which you can normally trust.
There are several options for those wanting to travel with bus from the airport to the center. With bus 12 and 21 you can travel to a station in the vicinity of the EU Parliament and the Luxembourg garden. This is probably one of the cheapest way of getting to the city center. For more information, visit www.stib.be.
If you want to have a private driver waiting for you upon arrival, find more information and book such a transfer from Viator.