Not a stupid question at all bro...in fact, i figured i should know this too so I dug out the old Jorge Cervantes Growers Bible and looked it up.
There are two types of nutrients...Macronutrients and Micronutrients.
Macronutrients are the nutes that plants use the most. The numbers(etc. 12-3-5) are the (N)Nitrogen, (P)Phosphorus and (K)Potassium percents of the fertilizers in the mix.
Nitrogen is required in high levels during veg growth and lower levels during the balance of life??? I guess flowering.
Phosphorus is used the most during germination, seedling, cloning and flowering. "Super Bloom" ferts have a high level of Phosphorous.
Potassium is used at all levels of growth. Soils with high levels of Potassium increase a plants resistance to bacteria and mold...(in the roots I am guessing, not bud mold)
Before talking about Micronutrients, here are some secondary nutes that are also used by the plant in large amounts. These are Magnesium(Mg), Calcium(Ca) and Sulfur(S). Jorge says that rapid growing pot plants are able to process secondary nutrients faster than they can be given...normally. These are normally present in ground water so be careful adding to much to water before you know its values.
All it says about Magnesium is that MJ uses alot of it and deficiencies are common. It says that extra Mg is generally not harmful and can inhibit calcium uptake.
All it says for Calcium is that the plant requires nearly as much as other macronutes. Calcium is fundamental to cell manufacture and growth. Deficiencies are uncommon indoors.
Many ferts contain sulfur and it is seldom deficient. Nutrients combined with sulfur mix better in water. Sulfur is an essential building block for many hormones, proteins, and vitamins including B1.
Now to the Micronutrients...they are also called trace elements, and they must be present in minute amounts and are essential to chlorophyll formation. They are very easy to overapply. They are Zinc(Zn), Manganese(Mn), Iron(Fe), Boron(B), Chlorine(Cl), Cobalt(Co), Copper(Cu), Molybdenum(Mb), and Silicon(Si). Basically it just says that these are in the soil, so they needed to be added to hydro water, but other than that they are used in very small amounts. Thats basically, should be what you need to know.