Most trains from Charleroi to Brussels stop at Brussels Midi/Zuid and then Brussels Central.
From Brussels Central, take the metro to De Brouckčre (next stop) or Sainte Catherine (one more stop).
If your train goes not go further than Midi/Zuid, you can either take a connecting train to Central or the underground tram to De Brouckčre.
(There is also a coach going from CRL to Brussels Midi)