The Uno has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analogue inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. There are 3 different options to power the board: via a USB cable, an AC-DC adapter or a battery.
A series of peripheral boards, known as shields, are available to plug into the top of the main Arduino PCB, providing an interface to components for a gamut of applications, including the Motor Shield, which enables the control of DC motors and read encoders, and the Ethernet Shield for connectivity.