I slipped down stairs 3 days ago. have swelling and bruising on the outside of my left ankle starting on the joint making almost a band shape to the back of my foot, left side of heel to pinky toe. foot is kinda numb and very cold to touch. what now?

Seek medical care : Given the traumatic history that you have given, I would recommend seeing a doctor and getting X-rays. If not right away go to the emergency room if you have insurance. I would recommend staying off it until evaluated. I would initiate contrast bath at this stage of the injury. Hot and cold soaks.

Ankle sprain: The most important question is are you able to bear weight (walk) ? If not, an X-ray may be needed. Otherwise, ice packs and elevation and ace wrap since it's most likely a sprain.