Yes, English grammar in terrible. But it has to be, because word meanings often depend on the grammatical constructions in which they are used. It specifies how sentences are built to make sense, identifies the meanings of individual words in a sentence and explains relationships between them, and gives you a set of rules for speaking and writing. Careful study of typical grammatical structures helps us to understand how meanings are created in English, and the ability to use such structures correctly and confidently is a huge step on the road to effective communication in English. Grammar is very important, but it doesn't mean that it has to be difficult.