The public transportation in Brussels is fine, and you can easily get around using it. The most important and frequently used mean of transportation is the metro, and there are 4(6) different metro lines to choose between when in Brussels. The most important metro stops as a tourist are: Gare Midi (main railway station) and Bourse/Beurs (Grote Markt). Tickets can be bought on the different stations and it is better to buy them beforehand. Tickets can be bought from the drivers, but that makes them quite a bit more expensive, so do it beforehand instead.
If you have validated your ticket it is valid for one hour (so called Jump ticket).
Brussels public transportation prices
Single ticket: 2 Euro
5 journeys: 7,50 Euro
10 journeys:: 13 Euro
Day pass: 6 Euro
Ticket for bus to and from Brussels airport: 3,50 Euro (line 12 and 21)