Arduino Uno is a microcontroller board based on the ATmega328P. It has 14 digital input/output pins (of which 6 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 needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.. You can tinker with your Uno without worrying too much about doing something wrong, worst case scenario you can replace the chip for a few dollars and start over again.
The CNC Shield v4 is made for the control of 3D printers, milling and engraving machines. This version of the shield has 1 motor driver less than its predecessor, but is more compact and has room for an Arduino Nano. This board has 3 sockets for the installation of stepper motor drivers such as the A4988. Only 2 channels per motor are required to control this motor. There is also a connection for 2 end-stop switches per motor.