Electrophoresis is a separation technique based on the charges on molecules. A mixture of substances is exposed to electrical field. Substances that are positively charged at a given pH will move towards the cathode (negative electrode) whereas negatively charged substances will move towards anode (positive electrode). The migration of substances depends on the charge of molecule, size of particle, molecular weight, etc.
Agarose gel electrophorsis is a type of gel electrophoresis which uses agarose as a matrix. Agarose is highly purified agar which occurs naturally as a polysaccharide made up of repeating unit of agarobiose.