Humans are omnivores that require a varied diet to stay mentally and physically healthy. They should be fed other organic organisms, preferably ones from their home planet.
One interesting thing about humans is that they have adapted to eat food that has been cooked, rather than raw. This essentially kickstarts the digestion process and allows for increased nutrient uptake. Some plants can be fed raw, others cannot. Meat should not be fed raw unless it is freshly killed and free of parasites.
Food for organics goes bad! If you see mold, it is NOT like rust, you can't just scrape it off! If you see mold, it has most likely permeated the entire food item, and I don't think I should need to explain why you shouldn't feed your humans rotten or moldy food.
Humans, like other primates, ancestrally lost the ability to synthesize Vitamin C. However, Vitamin C is still necessary for them to function, and a deficiency can cause their bodies to fall apart. Fortunately, many fruits are high in Vitamin C, and most humans are happy to eat fruit.
Speaking of fruit, there is a database on which Terran fruits are safe for humans to consume and which are poisonous. Same with other parts of plants, as well as fungi.
Perhaps because of the sheer variety of things they can eat, some humans can be picky about what they will eat. As long as you can find sources of carbohydrates, fats, protein, fiber, and vitamins and minerals that your humans will eat (you may need to experiment with combinations and cooking methods - for example, some humans don't like raw vegetables, even ones that are safe for them to eat, but will eat them cooked and mixed with other food), your humans should be fine.
Like other organics that use water as a solvent, humans should have access to fresh, clean water at all times.
