Can someone explain the story of inception..its so mind boggling..and i couldn't understand the movie..!!!?

All that i understood is..leonardo can get into others dreams and implant an idea, but his personal life part is so confusing, and that small spinning thing how is that helping him to find out whether its reality or dream? and does he achieve his target? and the last scene was he still dreaming? and how did he wake up? wat did that old guy tell him...!!! plessssee explain...my head is breakin..!!!!