The above animation shows how a 555 timer works as an oscillator. This is useful in understanding how the current flows in the circuit and the voltage drop at various points in the circuit. In the above circuit animation, the resistors and the capacitor creates charging and discharging time. During the charging time the capacitor is charged and during the discharging period, the stored charge in the capacitor flows out of it and into the light bulb. As you can see the bulb gets on slowly and slowing turns off.
The frequency of oscillation of the timer is set using the resistors R2, R3 and capacitor C1. The formula to calculate the oscillation frequency is,
\(F_{osc}=1.44/(R_3+2R_2)C\)
The circuit is explained in much more details in the tutorial How 555 Timer works in Astable Multivibrator Mode. There the full mathematical derivation of frequency of oscillation, charging and discharging time, time period etc are provided. Once you have understood how the circuit works and the mathematical expression of frequency you need to calculate Resistor and Capacitor values to generate Square Wave.
Learning 555 timer can be useful. 555timer can be utilized in many electronics projects. It can be used to generate different types signals which may be required in your projects.
I hope this animation was helpful in understanding 555 Timer Oscillator.
