It includes an extensive component data base that can be inserted into the circuit. Each one has its respective electronic properties: resistances, voltage sources, diodes, transistors, gates, LEDs, bridges, etc.
Qucs also allows you to calculate the electronic properties of different transmission lines and radio frequencies through a module known as QucsTranscalc. It manually introduces the values of the different parameters to obtain a precise result.
Another similar tool to Qucs is Kicad, although this one is much more developed. It's your choice.