From childhood You always saw blinking of lights..right??And after getting older and studying electronics or computer hardware basics you always saw the term "clock Pulse" ...right?? So this clock pulse is nothing but a square wave, which is exteremely useful for sequential circuits. Those LED chains which you saw in your childhood are actually build using such sequential circuits.
Now a rectangular or square wave can be generated using 555 IC and simple RC components.We will see next.
Below is a link to make a 555 astable clock generator. Click on the below image to open it.
Again you can obviously make a custom made printed circuit board for it to make it more professional.
The 555 timer IC can be used with a few simple components to build a monostable circuit which produces a single output pulse when triggered. It is called a monostable because it is stable in just one state: 'output low'. The 'output high' state is temporary. Below is a pic of a monostable circuit.
Monostable Circuit for a 24 sec timer which will act as an indicator to wash your hands Do you know? 7555 is the CMOS version of NE555 and NE556/7556 is a Dual timer IC
You can use this online calculator tool for calculating 555 astable and monostable circuit parameters