When a dragon found me, i was indeed scared [censored]less. But it never landed, so i tried shooting it. Why can't i ever hit the damn dragon with my bow?

Well the bow isn't a railgun and the arrow projectile is affected by travel time and gravity so you need to lead your target and compensate for drop. Other than that, eventually you get an ability that will make the task of dealing with dragons easier.

It helps with a companion i believe, to distract the dragon or help shoot it down, i am a pure warrior so need help bringing it down

Shoot a fireball spell at it. It has longer range than a bow I believe