M2 has an XBee-compatible form factor socket on the top of the processor board. In other words: two 2mm pitch x 10 pin headers spaced 22mm apart. You an read more about XBee modules on Wikipedia
There are LOTs of modules that fit this socket, with many different functions. WiFi, BLE, GSM, LTE, Ethernet, etc.
When connecting a XBee-compatible form factor socket to M2, makes sure that is is oriented so that pin 1 (+3.3V) is at the corner nearest the USB socket as shown here:
For an image showing the pin names of the XBee socket on M2, click here.
M2 has a USB connector that can act as either a HOST or DEVICE depending on your code.
M2 uses Native USB port only. To print something to the Serial monitor, you'd need to use this command: