Step 6: Pin outs
Digital pin 1: Port A, Bit 0 = PA0
Digital pin 2: Port A, Bit 1 = PA1
Digital pin 8: Port A, Bit 7 = PA7
Digital pin 9: Port B, Bit 0 = PB0
Digital pin 10: Port B, Bit 1 = PB1
etc. etc. etc.
The analog pins are defined like the above, but the ADC pin with the first register (after the alphabet; Port A is before Port B etc.) what has ADC and the first bit (bit 0) is analog pin 0, the ADC pin with the first register what has ADC and the second bit of that register is analog pin 1.
PWM pins have the same pin numbers as normal digital pins. To see witch digital pins are PWM enabled, look at the pin out in the datasheet. At some pins, there will stand "OC#@" There the # is a number and the @ is a letter. The @ is not always present. So on every pin there is stand OC + a number + a letter (not always) has hardware PWM.
Serial pins are defined as RXD and TXD. Some times there are multiply hardware Serial lines. If this is present, TXD and RXD are Serial, TXD1 and RXD1 are Serial1 etc. etc.
To see that pins have I,,2,,C, SPI etc. look at the datasheet and search for the corresponding pins (I,,2,,C: SDA and SCL etc.)
The interrupt pins are labeled with INT#, there # is the number of the interrupt.
If anything is unclear, post a comment.