The 556 is a 14 pin dual version of the 8 pin 555 timer IC
555 / 556 Timer Pin Diagram
Astable - producing a square wave
Monostable - producing a single pulse when triggered
Bistable - a simple memory which can be set and reset
Buffer - an inverting buffer (Schmitt trigger)
Supply voltage 4.5V - 16V
Note for low voltage below 4.5V you need to use the CMOS version LMC555 IC (1.5V - 12V)
The output of a standard 555 or 556 can sink and source up to 200mA.
555 Timer Modes Explained