Notice the "H". That's our friend the Hydrogen atom. The "C" is Carbon. Fuel Carbon chains are usually C7H16 through to C11H24.
C7H16 means 7 Carbon atoms with 16 Hydrogen atoms. Heavier chains like C14H30 are used as diesel fuel. Carbon chains above C20 are tars and heavy oils. The lightest chain is CH4. That's 1 Carbon and 4 Hydrogen (Methane).
We burn the mixture somewhere around C9H20 in our internal combustion engines. Chains of this weight are used as our fuel because they're in a liquid state at normal temperatures, easy to store and transport. They also vapourise easily. Pour gasoline on your driveway and watch how fast it evaporates. In order to burn the gasoline it must be transported from your tank to the combustion chamber. There the gasoline is mixed with the air from your air intake, vapourised, compressed, and BANG...ignited. This process takes place very quickly and continuously to maintain the cycle of the internal combustion engine.
Why the science lesson? To make a point; YOU ARE ALREADY BURNING HYDROGEN AND OXYGEN IN OUR INTERNAL COMBUSTION ENGINES! The difference between this and pure HHO is the carbon atom. The carbon that's left behind is what causes engine sludge, deposits and carbon build up, poor performance, pollution, and the inevitable downfall of our cars. The fact is that most cars don't make it past 200,000 miles without meticulous maintenance. All too often carbon is the culprit.
This HHO generator dissociates water molecules through the process of electrolysis. H2O (2 Hydrogen atoms and 1 Oxygen atom), when separated becomes a combustible, clean burning gas rather than a liquid. The gas burns and vapourises the carbon and fuel leaving only steam.

This gas (Separate Hydrogen and Oxygen atoms) is fed into our engines via vacuum lines and/or the air intake lines. There it is added to our Fuel/Air mixture. In the combustion chamber the pure hydrogen and oxygen give our Carbon chains a much needed boost. The enhanced combustion of the gasoline means that less gasoline is required to power the car. The cleaner burn helps remove undesirable deposits of unburned Carbon atoms. The vapourised Hydrogen and Oxygen atoms blast carbon deposits away.
The Hydrogenerator system also adds water vapour into your engine. This is not a new idea. People have been using this trick for decades. The water vapour helps to slightly cool your engine. Heat is bad for your engine. Especially in mid summer. A cooler engine runs smoother, needs fewer fluid changes, and lasts longer than an overheated one. Common sense.

If you read and understood that, you are probably asking yourself the question

"Why haven't auto makers installed these on their cars yet?"

The petrochemical industry is very powerful and influencial, it would not be in their financial interests They work very closely with the Car industry, who in turn influence Politicians........... need we say more!