From left to right in that pic orientation. 6. INT (GPIO 1.8V) and 3.3V DC 5. SDA (1.8V) and SCL (1.8V) (i2c) Unnumbered circle from top to bottom: 5V DC + GND (for example to connect wireless charger, external chargers or extra battery pack). And the hole next to screw 13 is the rib for cover detection. Official documentation should be coming 'soonish'.