Starting from the left:
- SCK - this is the SPI data clock pin, connect to your SPI master clock out
- MISO - this the SPI data out pin, data is sent from the module on this pin. Data level is 3V but that is fine for 5V microcontrollers.
- MOSI - this is the SPI data in pin, data is sent to the module on this pin.
- REQ - this is basically what the nRF8001 considers the 'SPI Chip Select' pin, its an input
- RDY (ready) - this is the data-ready pin, an interrupt output from the breakout to the microcontroller letting it know that data is ready to read
ACT (active) - this is an output from the module, it lets the host know when the nRF8001 is busy
- RST (reset) - this is the reset pin input.
- 3Vo - this is the output from the onboard 3.3V regulator, you can grab up to 100mA from this pin.
- GND - common ground for data and power
VIN - 3-5 VDC input to power the breakout