Hi Neung, I've made some corrections to your essay. Any corrections I made are now in red letters. If you have any questions about what I mean, or would like a more detailed explanation on why something was incorrect, please ask. We'll try

It depends on context. boys- plural of boy boy's - possessive of one boy boys' - possessive of more than one boy

The correct spelling of "grammer" is "grammar". "Nazi's", if you mean the plural of Nazi, should be "Nazis" without the apostrophe. The "s" is part of the word. "Grammar Nazis" appears to be a vocative, so I would add a comma after it. Finally,