How to add a new target in Oracle Enterprise Manager 12 C
Well this task i am afraid it can not be described here, i mean it could but is to much to write and i will not re-invent the wheel.:)
 So i recommend you follow this article How to add a new target on OEM , i wrote this article with this purpose(help guys like you ! kkkkk ).
 i might get a down vote for my short answer ! but for those intrested  -- fell free to read the article !! And thare a lot's of them on Oracle Enterprise Manager 12 C .