How does current flow between two out of phase voltages?
Current will flow in proportion to the voltage difference.



Figure 1. Taking the red phase as reference and the green as the other phase the voltage across the load will simply be the difference in potential between the two phases.


  Whether two out of phase voltages can be considered as positive and negative terminals between current flows when load is connected?


As can be seen in Figure 1, the voltage difference alternates in polarity. The result will be a sinusoidal waveform.

This is simply the phase-to-phase voltage of a three-phase system.


The voltage will be given by \$ V_{P-P} = \sqrt 3 V_{P-N} \$.
The phase will be 90° lagging behind the reference phase-neutral.



  How does current flow between two out of phase voltages?


That depends on the load. For resistive loads the current will obey Ohm's Law. For inductive or capacitive loads the load current will depend on the impedance.

See also: phase voltage vs main voltage in three phase system.