JulH is correct. If you stay close enough to Gent-Dampoort you can indeed take the train from there and have to change in Gent-Sint-Pieters for going to Brussels, no extra ticket is needed for that. If you go to Sint-Pieters with the bus or tram you need seperate tickets, costing €3 per person. The ticket is valuable for 1 hour, you can change buses, trams as much as you like within this time slot.
SNCB – NMBS services trains in Belgium, De Lijn trams and buses in Flanders the Dutch speaking part of the country, both have their own tickets and selling points. If you have the plan using several times the bus or tram a De Lijn 10-ride card costs €16, magazine/tobacco shops sells them. STIB-MIVB is the company in Brussels servicing buses and trams with also it’s own tickets.