There are many general use transistors available. The BC558 is a PNP transistor and a heavy duty drop-in replacement for a 2N2222 or 2N3906.
The three terminals of a bipolar transistor are called the emitter, base, and collector. A small current into the base controls a large current flow from the collector to the emitter. The current at the base is typically one-hundredth of the collector-emitter current. Moreover, the large current flow is almost independent of the voltage across the transistor from collector to emitter. This makes it possible to obtain a large amplification of voltage by taking the output voltage from a resistor in series with the collector.