What you're looking at is called "passive voice". Basically, the subject of the sentence receives the action instead of doing it. So in your example, the subject of the sentence is "the words". However, they don't do anything - someone will learn them, and maybe it's you (or me!). So, "be learned" is how you tell us what happens to those words. If you mean the whole "the words to be learned" part, then you understand it as "the words which are to be learned". We use the "to be (verb)" pattern to mean an action which is expected. There are the words which are to be learned. You are to learn these words.

It is years since I studied grammar, Erkan, but essentially to be plus past participle is describing an action that will be done in the future. - a lesson to be ( that will be) learned, a race to be ( that will be) run on Sunday. A game to be ( that will be) played next week.