Paralleling transistor is useful when the amount of current, or power dissipation, in a single transistor is too high or heat sinking a single device is impractical.
The circuit shown has three terminals labeled B, E, and C. These are the equivalent of the base, emitter, and collector of a single transistor. The series resistors, R, are used to compensate for variations between the transistors and force them to share roughly the same amount to current. At full load, the value of R should be chosen so that the voltage drop across each transistor is about 200 mV. The current used for this calculation is the current through an individual transistor not the current though the group of transistors.