Why We Use 74HC595, 74LS595 Serial In Parallel Out Shift Register
The sole purpose of shift registers is to save the pins/ports GPIO of any microcontroller or microprocessors because 
every microcontroller has a limited set of pins, in order to extend the pins shift registers are used. For more details download datasheet 74HC595 shift register from here. Example if you need to run 16 LEDs from a microcontroller and your microcontroller has no 16 pins and you don’t want to busy all pins of microcontrollers then you can use shift registers. After download datasheet 74HC595 read carefully every pin description how it is connected and works. Using two shift registers 74HC595 and occupying only three pins at microcontroller Arduino example you can run all 16 LEDs at once. You can chained more 74HC595 to create more series of LEDs. It comes into given variants CD74HC595DW, CD74HC595DWR , CD74HC595E , CD74HC595EE4, CD74HC595M , CD74HC595M96
CD74HC595MG4, CD74HC595MT, CD74HC595NSR, CD74HC595SM96
Working Principle Of 74HC595 Shift Register
When we apply pulse to the 74HC595 then the bits in the working shift register moves to the left. Example as given here Bit 6 takes the value and stores in the memory which was already in bit 5, and then bit value becomes 5. Bit 0 takes the value from the DATA pin when rising edge of the clock data available at pin pushed inside the shift register.
74HC595 digital IC contains 8 bit serial in and parallel out shift registers that works on 8 bit D-type memory. Register has 3 state parallel outputs two clock pulses are used separately one for shifting data and another for storage memory register. To see how it works you need to understand the working of the chip for this you have to download Datasheet 74LS595 74HC595.
8-Bit Serial-In, Parallel-Out Shift
Operating Voltage Range of 2 V to 6 V
High-Current 3-State Outputs Can Drive Up To 15 LSTTL Loads
Low Power Consumption, 80-μA Max ICC
Typical tpd = 14 ns
±6-mA Output Drive at 5 V
Low Input Current
Applications 74HC595/74LS595 Used In
The shift register 74HC595 is used in various applications all over in digital applications, few of them are given below.
LED Control Systems : while working on LED application registers plays an important role in switching on and off to LED, large moving led sign board, scrolling led marquee boards are common these days.
Network Router and Switches : Networks Routers handles tons of data everyday to process it and store into hard drive, to switch between data and storage shift registers are used, because they have capability to occupy less pin on hardware and works parallel.
Computer Cloud Servers : Cloud servers hold the key information and storage data of websites and online applications, to keep data move from one location to another and storing, shift registers are used.
Heavy Power Infrastructure : Switching between power grid to another power grid and continue power supply is the major part of power automation so here shift registers hold the data serially and push it parallel to the selected devices to switch power grids.
Industrial Automation and Control : In industry all electrical and electronics based panels are integrated with shift registers that are common and important for any industrial automation. Robotics plays major role in automation and all devices and components of robots uses shift register chips.
Electronic Home Appliances: All electronic home appliances Microwave oven, water purifier, mixer grinder are equipped with shift registers because they need it to work with data stored inside it.
In the last above given details are just reference only it is highly recommended you need to download datasheet 74HC595 74LS595 shift register.
