The tactile button is a momentary switch. It is only only on when pressed and is off as soon as you let go. It is a common type switch or button on electrical circuits. Even though it is only on when pressed it can be coded so that it triggers something when pressed. Press to switch on and then press again to switch off.
The problem is that as it is pressed a circuit is made and there is an infinitely small bounce effect as those two bits of metal meet. It is called bouncing. It can be very pronounced if not taken into account and can cause all sorts of problems as it can’t work out if it is on or off or fluctuates between the two rapidly. To be avoided.
So there is a neat bit of code to correct that called ‘debounce’ and can reduce the effect quite considerably.
The buttons have four legs. They fit neatly on a breadboard. Use a 10kΩ resistor with it if using it with the digital pins.