You don't really need grammar to speak a language. Even, when you are a little kid, you start talking in your native language without knowing any single grammatical concept.
However, when you grow up teachers try to make you learn some concepts and rules which are in the structure of your conversation or writings. You know quite a lot of the grammar of Catalan or Spanish, why don't you use that in English?
Only grammar won't make you learn a language, but comparing the grammatical ideas that you already know with some essential gramatical concepts of English will help you a lot. And, what is more important, you will be able to understand and remember the grammar in an easy way.
Don't try to study these grammar sheets as something isolated from your language, but only finding similarities and differences you will learn and improve in both languages.
