The .1" headers are mounted on the bottom of the PCB for simple insertion into a breadboard. Pins labeled 5V/GND 3.3V/GND plug directly into the power lines.
When you plug this board into a breadboard you must be aware that the unused power and ground pins will short if they are inserted into a bread board row. To avoid this problem, orient the board so that the unused power pins are left off the side of the breadboard. You can also orient the board sideways and utilize both 5V and 3.3V at the same time.
USB v2.0 specifies a max of 500mA at 5V. The on-board fuse limits the current to 500mA. Board has a handy On/Off switch.
Comes as a bag of parts kit and is easily assembled if you can follow the silkscreen indicators and have beginning experience with a soldering iron. You will need to read the resistor bands or use a multimeter to determine the resistor sizes.