I can recognize many words that I don't know the meaning of. Why is that?

This often happens because there are some words that are very frequent, but which meaning can't be acquired until your level is higher. Common examples are grammatical connectors, like articles, conjunctions and prepositions. Since the purpose of this kind of words is to show how different elements of the sentence relate to each other, it’s not possible for our brain to figure out their meaning subconsciously until we already know most of the other words in the phrases in which they appear. And then we need to get exposed to enough of these phrases for our brain to figure out the pattern and therefore their meaning. This feeling of being familiar with some words but not understanding them happens even more if you watch a lot of content that’s above your level. For some of those words, you may actually be able to recall them and say them out loud before you know anything about their meaning. The meaning of these words will become clear once you are at a level in which you can understand the sentences in which they appear.