A LM7805 Voltage Regulator is a voltage regulator that outputs +5 volts.
An easy way to remember the voltage output by a LM78XX series of voltage regulators is the last two digits of the number. A LM7805 ends with "05" , thus, it outputs 5 volts. The "78" part is just the convention that the chip makers use to denote the series of regulators that output positive voltage. The other series of regulators, the LM79XX, is the series that outputs negative voltage. So:
LM78XX. Voltage regulators that output positive voltage, "XX"=voltage output.
LM79XX. Voltage regulators that output negative voltage, "XX"=voltage output
The LM7805, like most other regulators, is a three-pin IC.
Pin 1 (Input Pin): The Input pin is the pin that accepts the incoming DC voltage, which the voltage regulator will eventually regulate down to 5 volts.
Pin 2 (Ground): Ground pin establishes the ground for the regulator.
Pin 3 (Output Pin): The Output pin is the regulated 5 volts DC.
Be advised, though, that though this voltage regulator can accept an input voltage of 36 volts, it is recommended to limit the voltage to 2-3 volts higher than the output regulated voltage. For a 5-volt regulator, no more than 8 volts should be applied as the input voltage. The difference between the input and output voltage appears as heat. The greater the difference between the input and output voltage, the more heat is generated. If too much heat is generated, through high input voltage, the regulator can overheat. If the regulator does not have a heat sink to dissipate this heat, it can be destroyed and malfunction. So the two options are, design your circuit so that the input voltage going into the regulator is limited to 2-3 volts above the output regulated voltage or place a heat sink in your circuit to dissipate the created heat.
If you want to learn more about connecting a regulator in a circuit, check out How to Connect a Voltage Regulator to a Circuit
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