ARDUINO UNO REV3 is a microcontroller board based on ATmega328P (datasheet). It features 14 digital input/output pins (6 of which can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator (CSTCE16M0V53-R0), a USB connection, a power jack, an ICSP header, and a reset button.
It contains everything you need to support the microcontroller; just plug it into a computer with a USB cable or power it with an AC/DC adapter or battery to get started. You can tinker with your ARDUINO UNO REV3 without worrying too much about doing something wrong, in the worst case you can replace the chip and start over.
If you are interested in boards with similar functionality, you can find the following on Arduino:
Arduino Uno Rev3 SMD
Arduino Uno WiFi Rev2
