First,when the subject is plural,you have to use "do".
etc: 1.We do homework.2.They do something wrong.
Second,when the subject is singular,there are two situations.1,you have to use "do" after "I" and "You";2,you have to use "does" after other singular subject such as "he","she","it" and so on.
etc:1.I do not like apple.2.She does not like singing.3.It does not fit my feet.