Don't worry too much about what specific words to use here. There is nothing wrong with keeping the overall tone of the sentence as it is. You are actually talking about something general: when someone who understands imparts knowledge to someone who does not. This, by itself, is worthy of discussion, without jumping immediately into a specific form of the relationship.
Consider this rewrite:
When someone explains something they understand well to someone who does not share that understanding, they will tend to define it immediately (as if they were an encyclopedia), or else compare it to something else by analogy.
Versus something that merely replaces the words in question:
When a teacher explains to a student, they tend to go define it right ahead (like Wikipedia), or compare it with another thing ("family, the vital cell of the society").
In the first example, we preserve the general relationship between someone who knows and someone who does not. This subject is interesting and worth talking about as a general phenomenon, without needing immediately to narrow it down into one of its many specific forms (i.e., teacher/student, master/disciple, expert/novice, tradesman/apprentice, and so on).
All you need to do is polish some of the rough edges in the sentence, and you're good to go.
Of course, if you are writing in the context of a specific type of knowledge transfer, then you would be better off using the terminology most suited to that context.