As an native English teacher, I think that students spend too much time worrying about grammar.
That seems controversial, and it really is.
A child listens, then learns to speak. He learns to read and then he learns to write.
I bet he learned to speak before he even knew what the word 'grammar' means!
I live in Brazil and I have learned Portuguese day by day, without taking any classes. Basically, I read and I listen to people. So, how did I learn? I simply try to repeat what I hear and read.
My Portuguese is far from perfect, that's because I have nobody correcting me, I have no grammar to fill in those small errors.
Grammar is important because there are always some doubts that we have about what we hear or read. But, generally students focus on the grammar too much.
Students often have difficulty 'accepting' a structure as an example and copy it.
If you know how we say things, and you understand it, then repeat it and modify it. Just like you did when you learned your native language. Grammar, then, just fills in the gaps!
So, grammar is important because it gives the necessary structure to the language. However, it's not necessary to know all the grammar in order to speak the language.