Vitamin K does one specific, important job: it's essential for blood clotting, how your body stops bleeding after an injury, and it also plays a role in bone health. When intake is low, that's associated with easier bruising and slower clotting, though genuine shortfalls are relatively uncommon on a normal varied diet.
It comes mostly from green vegetables, with kale, spinach, and broccoli among the richest sources, along with some vegetable oils. Adults need around 120 mcg a day for men and 90 mcg for women. There's no established upper limit from food.
Two honest notes. Reliable intake data is thinner than for the well-studied vitamins, so this one is better understood than precisely tracked. And if you take a blood-thinning medication such as warfarin, vitamin K interacts directly with how it works, so any changes to your intake are worth discussing with your doctor rather than adjusting on your own.