Your Fusion 2 comes with a micro-USB charging cord, which is plugged into a charging port on the side of the device (underneath the wristband). With the charging cord plugged into that port, the other end can be plugged into a computer USB port, USB wall outlet adapter, or any USB power outlet of your choosing. 

Note: be gentle when plugging in and unplugging the Fusion 2 - no need to force the cord in or out of the charging port. If you're having trouble plugging in, make sure the cord is oriented correctly: