As you know, a battery is a device that stores energy that we can use in an electrical form. To form an electrical current, we want to create a flow of electrons. This can be done by utilizing an oxidation-reduction reaction. Basically, the oxidation process creates electrons, and the reduction process uses electrons. By connecting the cell together, the two reactions work together to generate a flow of electrons.

Now, at one of these electrodes of an electrochemical cell, the oxidation process occurs, and at the other electrode, the reduction process occurs. For a non-reversible electrochemical cell (for example, a non-rechargeable battery), the anode is where the oxidation occurs and the cathode is where the reduction occurs. At the anode, the oxidation that occurs has a net effect of generating and transferring electrons to its electrode, thus giving it a relative negative charge. At the cathode, the electrode loses electrons to promote the reduction to occur to give the electrode a relative positive charge. With the anode having a relative negative charge, and the cathode having a relative positive charge, there is a net flow of electrons, or current, between the two electrodes that can be used to do work outside of the system. Hope this helps!