First, concrete and abstract words are correlated with ideas in the brain. Then they form vocabulary and, as it grows, can be combined into phrases and sentences. In case of a native language, it's not necessary to study grammar to combine them. One has only to get used to say right words at the right place and time, picking them out from the memory and having the milieu as a natural corrector.
The other situation is when a person is learning a foreign language. Then the brain makes pairs of words: "stored (native) - new (foreign)". But as long as there's the need of grammatical transformations, it's incorrect just to replace one word with another when translating (like GT does it). So, in addition to new words, it's necessary to remember new rules (with inexplicable correlations with the native grammar). Some months/years/lives of putting all this in order - et voilà! Yet another peculiar mumbler has appeared!
This is not what 'i think'. This is just the translation of it.