has anybody got any idea how i start the companions quest?

Go to Whiterun, walk into the city. Make a left at the market area. Make a right at the dead tree, enter the Meadhall of Jorrvaskr, head right and go downstairs. Make a right and follow the hallway until you see Kodlak and Vilkas talking, then speak to Kodlak (Kodlak is the old man sitting).
Listen to thier conversation, it will explain some of the things behind the Companions. Any person in Jorrvaskr will tell you to speak to Kodlak, so you can just follow the arrow.

You mean the whole quest line? If so, travel to Pelagia Farm, just east of Whiterun. If this is your first visit to the town, you should either see a giant in the field, a giant in the field being attacked by the Companions, or a dead giant in the field surrounded by Companions. Talk to Aela (she'll speak first anyway, criticizing you) and you can inquire of the Companions. This starts the quest to see Kodlak Whitemane.

OTOH, if they are not there, go to Jorrvaskr and talk to Aela or somebody else, or simply head downstairs and find Whitemane. He's usually in conversation with Vilkas.