Hello, please can anyone explain me the difference between:
Parallel-in/Serial Out
Serial-in/Parallel-Out
Shift regsiters ? If you can give some examples I can understand easily couse I cant understand a da*n thing that I searched on the net.
To save pins on the cpu, it can talk to add-on chips with a serial protocol.
With a serial-in/parallel-out you can add 8 (or more) digital output pins at the cost of 3 cpu pins (data, clock, chip select). Good for a lot of leds 
With a parallel-in/serial-out chip you can add 8 (or more) digital input pins.
Parallel - lots of bits at the same time.
Serial - one bit at a time.
So with a shift register you can load lots of bits into it and clock them out one bit at a time. That's parallel in serial out.
OR
Input the values one bit at a time and have them appear on different pins.
You may also see some reference to a "latch" built in to parallel out shift registers. This is like a memory freezing the outputs so you don't see a succession of logic levels as a bit travels from the input to it's required output pin.