HHO isn't the conventional way to write H2O (dihydrogen oxide), but it's not exactly wrong, just as it's not wrong to write water as hydrogen hydroxide, HOH. In certain chemical equations, it's convenient to think of water that way, e.g., 2Na + 2HOH --> 2NaOH + H2.
I don't dispute that there's a lot of woo-woo misinformation about the uses of hydrogen as fuel; but in the late 70s there was serious research into using hydrogen with gasoline to significantly increase fuel efficiency. Prior to Compound Vortex Controlled Combustion (CCVC) and electronic fuel injection, a bit of hydrogen injected along with gasoline into combustion chambers allowed carburetors to use a very lean mix of fuel/air for more efficient burning. Hydrogen will ignite and in turn would ignite the gasoline, with very lean fuel/air ratios. I read up on this too many years ago to remember all the details, but apparently the CCVC approach won out with auto manufacturers. Engineers apparently never got past the problems of electrolyzing H2 as-you-go to mix in the fuel injection to make cars run more efficiently--all woo-woo claims to the contrary.
I'm highly skeptical of the conspiracy theorists that claim the hydrogen technology was/is suppressed. The auto industry seems too competitive for that to be feasible. In the 70s and 80s, the research looked promising, Hydrogen isn't that hard to make from water on an industrial scale, given abundant cheap electricity from also-promising solar and wind technology; but the engineers never were able to get past the problems of H2 storage, which is more complicated than one might think.
Now if someone has serious research (excluding miraculous sales claims) to show me my information is out of date, I'd love to see a link to it.
All that being said, since the OP hasn't yet said what s/he's trying to do, we're just speculating. Back in high school, I made a homemade H2 generator to fill baloons; but I used a chemical approach. I played with electrolysis, but didn't know how to make or use a DC power source back then; so I gave up on it.