"Hence" is similar to "therefore". Both hence and therefore are adverbial conjunctions which are used to join independent clauses, Adverbial conjunctions tell the reader the relationship between the two main clauses, in this case, that of cause and effect. i.e. because we must use words, we must inevitably use concepts..

1) Hence means why something is happening. For example: She is angry, hence the screaming. 2) Corrections for your writing: "The above sentence comes from one of my English textbooks aimed at improving reading level. I cannot understand what "hence concepts" means or why "concepts", which is a noun, is proceeded by "hence", a verb?" Your sentence was a run-on and needed to be broken into two sentences. Please let me know if you have any more questions!