Can someone explain warframe elemental damage combos simply?

four base elements: heat, cold, electricity, toxin. any two make one combined element: heat + cold = blast electricity + toxin = corrosive heat + toxin = gas cold + toxin = viral electricity + heat = radiation cold + electricity = magnetic the part that trips people up is they combine in mod slot order, top left first, and the weapon's own innate element gets added after your mods. so put the pairs you want next to each other. viral and corrosive together is what most builds go for, that's cold, toxin, electricity, toxin in that order.