First, I think you should use iTalki's "notebook" function for this kind of question.
It should be:
Is this sentence's grammar correct. Can you correct it please? (grammar是不可数的名词，因此it, 还不用 ,)
I think that English grammar （不要"the"因为the的意思是具体的，English grammar 是一般来说的）is like the rules of Math. If you want to improve your grammar， you must practice everyday so we won't forget what we have learned.
(比较地道的话。要是说“learn it”，就我认为你已经学完了或者你已经成为English grammar的大师。