Languages would not even exist and we would not be able to communicate meaning if languages weren't distinguished by grammar or structure. However, some people are aware of their language learning process; others aren't. When children learn a first language at home, they don't necessarily learn grammar, but they still form meaningful, structured sentences, even if they were over-simplified. That's because language is innate. Language acquisition isn't limited to an academic setting of course, but if you learn a lanuguage, let's say by watching movies and listening to music, you don't necessarily learn the grammar, but you acquire it subconsciously nonetheless, because your mind stores the repetitive patterns in a language and starts to form grammatical generalizations. So to answer your question, yes, grammar is absolutely necessary. How you "learn" or "acquire" grammar, however, is trivial.

Though I am bad at Grammar but I do believe that it is so necessary to learn any language. It gives the important bases to form sentences from the simplest to the most complicated ones.

Not at the beginning, no.  Learn grammar after you have a solid foundation in the language.  Don't study it, use it as reference instead.

agree to guys who advise not to be gramma-nazi having just started learning languages. 

but for God sake don't neglect it completely
because "Yes I knows these language and are you know it?" is - I guess - not the way you want to speak in future

i think Grammer is the foundation to learn English.but when you speak to  English native speakerS,you will find just few words can make them understand you even you use the wrong Grammer.