> I am left handed and  i don't understand why some people makes it as an issue. Maybe they think it's difficult, but for me whose used to it, such thing isn't a big deal. If you are left-handed, please share to me your thoughts.    

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* Correction:     Student's sentence        Corrected sentence        Grammar explanation       Better sentence    

I am left handed and  i don't understand why some people makes it as an issue. Maybe they think it's difficult, but for me whose used to it, such thing isn't a big deal. If you are left-handed, please share to me your thoughts.   

I am left handed and  i don't understand why some people makes it as an issue.
I am left-handed, and  I don't understand why some people make it an issue.
Place a comma (,) before and when it's connecting two independent clauses. 
Keep in mind the basic subject-verb agreement rule: a singular subject takes a singular verb, whereas a plural subject takes a plural verb. In your sentence, "people" is plural, therefore your verb should also be in its plural form - "make". 

 Maybe they think it's difficult, but for me whose used to it, such thing isn't a big deal.
 Maybe they think it's difficult, but for me who's used to it, such a thing isn't a big deal.
Who's is a contraction on who + is. or who + has. Whose means "belonging to whom".  Another explanation: Whose is usually followed by a noun. If there is no noun or an article, use who's, which is the case of your sentence. 

If you are left-handed, please share to me your thoughts. 
This sentence is correct!