The spelling is <em>grammar</em>.

"Is it important to know all the grammar in English to speak like a native speaker?"

Well, let me ask you: do you know all the grammar in Arabic? Or do you speak Arabic very well, even if you can't technically explain how the grammar works?

It's the same for native English speakers.  However, as a learner you need to pay more attention so it'd be a huge mistake to ignore the grammar - we certainly notice!

If you actually wrote down exactly the words that native speakers have spoken, you may often find the result very ungrammatical. Native speakers often do not have perfect grammar in spoken language.

There are more formal situations in written language where grammar becomes more important.

It is easier to communicate without perfect grammar by speaking rather than by writing because there are usually more clues to meaning in a speaking situation compared to a piece of writing.

In my opinion, if you wish to speak more like native speakers, it is better to try to just imitate native speakers (that is the oldest and most basic form of language learning), rather than study grammar.

...and what native speaker anyway? USA, UK, Irish, Indian, Australian, Kiwi, S.African, +  +  + ?

Don't think about it, the anwer is: no.

Writing and speaking are different things. Perfect grammar doesn't make you a native speaker. 

I know some languages.that 's why i said english is easy than others.my english is poor,right.for example russian is more diffucult.italian language too.:)))))

grammar is like ...to me a a thing with which I reduce the chances to ask some of the basic questions. although grammar is important, u cannot rely on it. asking quesions when you have native-speakers with you on a daily basis is vital to English improvement. so....to conlude, its not so much an important thing as really asking native speakers daily conversational questions by which u pick up more english sense.