A regulated power supply is very much essential for several electronic devices due to the semiconductor material employed in them have a fixed rate of current as well as voltage.
The 7805 voltage regulator produce at its output a fixed +5V but in order for the IC to work effectively, the input voltage must be greater than 5 V. Remember, it is essential and very important to power a digital circuit with this kind of IC. If you are looking for a regulated -5V at the output you need to use its negative counterpart IC 7905.
You can see from the above picture the volltage regulator pinout. the input where you connect the input voltage with respect to ground GND, and the Output where you tap the +5V. Be careful to connect the IC correctly to avoid damages.
See on www.electronicshub.org