Can any of you give me a hint on how i get the quest to start dragon born? do i need the main story complete?

Try this. It will help.

http://www.gamesas.com/topic/1427554-how-to-start-the-dragonborn-dlc/

Some cultists should spawn near you starting the quest.

You have to have already visited the greybeards before they will spawn though.

In my game they spawned within a minute of exiting breezehome after loading the save.

You just need to finish one of the Greybeards' quest which is to find this one item (forgot what it's called) and just walk around until a group of Cultists' attack you. Loot the leader's note and read it then travel to Windhelm. Talk to the captain of one of the boats and ask him to take you to Solstheim. You pay a fee or "politely" ask him to take you there.