For plants and humans to survive, we need many different minerals incl Iron, Zinc and so on. The problem is that these minerals are not organic. So if you have an iron shortage, you can't just shave some iron off a pole and drink it right? Your body and cells will reject it because it is inorganic.
Humic and fulvic acid act as chelators, or claw molecules. This means they form complex bonds with inorganic minerals which allow those minerals to become 'organic' ie penetrate plant and human cells.
Humic acid attracts minerals and deposits them in crystals around the root zone of the plant for uptake. It is used as a soil conditioner and the effects of treating soil with humic acid lasts for years, cutting down on one's use of synthetic fertilisers. It also has a 40% carbon content - the primary component of all Earth life.
Fulvic acid is a much smaller molecule, so small that it actually carries minerals and nutrients directly into the plant cell's metabolic centre, spurring growth. It has a high iron content (you'll be able to smell it when you open the bottle) which helps with chlorophyll and a plant's ability to turn sunlight into energy.