Sinusoidal PWM running BLDC motor in open loop
What does sinTable[index] * pwr mean, in terms of power?


The AC motor voltage waveforms are created from DC using PWM. pwr scales the sine table values so that at full power the PWM ratio varies from 0% to 100%, which creates a sine wave that goes from 0V to 12V (when using a 12V power supply). If the value of pwr is reduced then the amplitude of the sine wave is reduced, so the motor gets less AC voltage and draws proportionally less current.


  what is the logical relation between the Pout and the index used for
  choosing the discrete value of the PWM in the sinTable vector.


There is no relationship between the index and output power. The purpose of index is simply to create a time-varying sine wave of nominal amplitude (-1 to +1) which is then shifted and scaled to produce a range of PWM ratios that varies from 0-100% at full power.


  There is a point I really don't understand, when pwr is high the BLDC
  motor takes currents like 0.8 A at 12 V.


This is to be expected. Your motor has an internal resistance of 5.5&ohm; per phase (11&ohm; between any two terminals). At 12V the voltage applied per phase is 12V peak-to-peak, which equals 4.24Vrms. Current = voltage / resistance so the rms current per phase is 4.24V / 5.5&ohm; = 0.77A, and power = voltage x current so each phase consumes 4.24V * 0.77A = 3.26W. 

Since all 3 phases are powered similarly the total power consumption is 3.26W * 3 = 9.78W. Current = power / voltage, so the expected DC current draw from the power supply is 9.78W / 12VDC = 0.815A.