I 我,主格,做主语,I will teach you...
my 我的,形容词性物主代词,作定语,my book
me 我,宾格,作宾语,tell me
mine 我的（东西）,名词性物主代词,作名词用,代替前面提到的东西 ,
Your pen is here,mine(my pen) is there