Vocabulary is always a difficult point for language learners, even for native speakers. Understanding which words belong to which categories can help. In order to understand the language, understanding grammar is a big help. However, to understand grammar, you have to know what everything is!
Making things more difficult is the messy, slippery nature of the English language. Some words are used in many different ways. The word "well" can be a noun, a verb, an adjective, and adverb, and an interjection. "Set" is a verb, noun, or adjective, depending on its use. "Fast" can be a verb, adverb, noun, or ajective ("People fast fast during the fast fast." — in order: verb, adverb, adjective, and noun).
A lot of verbs become nouns. "Take," for example, can mean an attempt at a movie scene ("We did it in one take!"), an amount of money that is made ("What was your take of the profit?"), or an understanding of a situation ("What was your take on the disagreement?").
The word "as" is used as a conjunction, preposition, and adverb. Figuring out which one it is can be very difficult sometimes.
The following page helps to understand the categories.