Johnson Davies shared detailed instructions of how to build an ATSAMD21-based computer on a prototyping board using a 32-pin ATSAMD21E:
If you’re looking for something more powerful than the ATmega328 in the Arduino Uno a good choice is the ATSAMD21. This is an ARM Cortex M0+ processor with up to 256KB flash memory, 32KB RAM, and a 48MHz clock, so it’s substantially better equipped than the ATmega328. In addition it has a USB interface built in, so there’s no need for a separate chip to interface to the serial port.
Arduino have designed several excellent boards based on the ATSAMD21, such as the Arduino Zero or smaller-format MKRZERO. However, these boards are an expensive way to use an ATSAMD21 as the basis for your own project, and they probably include many features you don’t need.
More details on Technoblogy.