Water is a molecule. In this case, the molecule is composed of two elements that are bonded with an electromagnetic force. The elements are hydrogen and oxygen. In a single molecule of water, there are two hydrogen atoms bonded to one oxygen atom. Water, unlike oil is called a polar molecule. It is polar because each side of the water molecule has an opposite charge, hence it has two different poles, a negative and a positive.
Electrolysis is a method that is used to break away the bonds holding the hydrogen atoms to the oxygen atom. If you can use an electrical current and pass it through a solution of water, you will overcome the bonds that hold the water molecule together. By passing more current, or by altering the design of the electrolysis cell, you can increase the decomposition of the water molecule (more hydrogen output).
Electrolysis releases hydrogen and oxygen from the water in a ratio of 2 parts hydrogen for 1 part oxygen. This ratio is extremely flammable and extremely dangerous under the wrong conditions. Electrolysis gas is known as e-gas, ortho hydrogen, or HHO. Electrolysis gas is not the same type of hydrogen that is in high pressure liquid hydrogen containers. Under the same conditions, refined compressed hydrogen burns slightly slower than the hydrogen produced from electrolysis. Compressed hydrogen is known as para-hydrogen while e-gas is known as ortho-hydrogen. Ortho hydrogen burns faster. Most of the gas produced from electrolysis or similar means is ortho-hydrogen.
Standard electrolysis uses low voltage and high current to create hydrogen gas. This type of simple electrolysis is commonly called "brute force electrolysis." The name implies that it takes a lot of energy to create hydrogen. This process is outdated, as new processes have been invented by many different inventors. The new inventions consume very little power compared to brute force electrolysis. Brute force electrolysis will always have it's place because it does not require special electronics, or complicated electrode designs. All that you need for brute force electrolysis is solvent based water, some large electrodes with a lot of surface area, and lots of amps. 12 volts seems to work very well for brute force electrolysis. Higher voltage does not normally produce higher yields, unless you place the electrodes very close together in which case the electrical fields help to physically pull the water molecule apart. Extreme caution has to be exercised to prevent shorts across the electrodes, they should be fastened solidly in the container to prevent explosions, or damage to electrical equipment, battieries, etc.