What is the meaning that electric charges flow from high to low potential till both acquire same potential? I was reading about electric current and circuits. I read in my book that electric current is caused when charges flow from high potential to low potential till they both acquire same potential. So my first question:

What is being referred to by 'they'?

Now, continuing my question, assuming that they refers to the positions. Now, my second question:

How come two positions in an electric field which initially have
  different potentials acquire same potential?

Maybe I am not understanding this correctly. Please help.
 A: Imagine two conducting spheres with charge on them which are at different potentials.
if you now connect the two spheres with a conductor, charges move until the potential of both spheres is the same.
Think of two tanks with water at different levels above the floor.  The tanks are connected with a pipe.  Water will flow out of the tank with the higher level of water into the one with the lower level until the level of water is the same in both tanks.
A: To answer your first question, "they" indeed refers to two different positions.
Two different positions in space that have initially different potentials can achieve equilibrium by attaining the same potential. To see how this might be done, imagine you have a box of free electrons and let's say the Coulomb interaction between themselves is weak compared to external fields. Next apply an electric field $\mathbf{E}(x,y,z)=E_0 \hat{x}$. Now the front side of the box has a higher potential energy for electrons than the rear. This will cause the electrons to move in $-x$ direction and accumulate on the rear wall. The accumulated negative charge on that wall will again create another electric field in the opposite direction of your applied external field $E_0 \hat{x}$. As long as the new field created by electrons hasn't achieved the same strength as $E_0$, electrons will continue to flow to the rear and make the response field stronger. Once the two fields balance each other out, the total potential of these two will be zero and the rest of the electrons in the box will continue to move freely and randomly so in general their net current is 0.
In classical diffusive regime (i.e. carriers collide with each other a lot), "potential" here should in general refer to electrochemical potential, which includes both the chemical potential of electrons and the electrostatic potential. Roughly speaking, difference in chemical potential causes diffusion current (very much like how sugar dissolves in water and the solution achieves uniform concentration) and difference in electrostatic potential (i.e. electric field) causes drift current (the Ohm law $\mathbf{j}=ne\mu \mathbf{E}$). The sum of these two is the total current. When the total net current is 0 in a region, the electrochemical potential in that region is the same everywhere (but not necessarily electrostatic potential or chemical potential alone).
