plz i need the description of the output/input pins of arduino uno ineed help thnxxxx 
It's all in the datasheet:
Summary:
2 digital headers D0 to D13: 14 digital IO pins, several with dedicated hardware support for: Serial IO (D0/D1), SPI Comms (D11-12-13, D10), Hardware interrupts (D2, D3), Pulse Width Modulation output (D3,5,6,9,10,11).
Analog header: 6 analog input pins A0 to A5, also used as general digital IO pins.
"upper" digital header also contains A4/A5 which support I2C comms.
"upper" digital header also contains Aref, an external input for the ADC unit.
barrel jack for power, 7.5V to 12V, can support up to 800mA of current (at lower voltages)
USB 2.0 for connection to PC, can supply 500mA of 5V current
Power header:
- IO reference pin connects to 5V
- 3.3V supply pin (~150mA current available)
- 5V supply pin (up to ~500mA or 800mA of current available). Possible to use as input, requires adding a diode, 1N4001 for example, from 5V (anode) to Vin (cathoode) to avoid reverse driving the 5V regulator.
- Vin - barrel jack voltage after passing thru reverse polarity protection diode
thank u 
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thank uuuuuuuuu