I cut my right ring finger open on glass about 3-4 days ago.. it is now numb, & there is a but of tissue exposed on the wound& if i touch it's pain?

Seek medical care: You should see a doctor quickly. You've likely injured a nerve, causing numbness. I am also concerned about glass fragments in the wound and the possibility of infection. Your wound needs to be treated professionally.

Ring finger: You should check it out. May have a piece of glass in there or an infection. Make sure also that you are up to date with your tetanus shots

See a doctor.: Likely too late for stitches but if you did cut a nerve not too late to check and repair it.

Keep the wound clean: Hope you had Tetanus Vaccine within last 5 years.. 3 days old wound, as long as it is not infected, you can mange by keeping the wound clean and applying Sterile dressing and topical antibiotic ointment. The pain is normal. Numbness is also ok as there is damage to the nerves (Tip of finger has great nerve ad vascular supply). Sensation may return. If any doubt get examined.

Expected: Numbness is expected because nerves get futon the injury. If there is a lot of exposed tissue, or the area is reddened or painful, you should see a doctor. You also need a tetanus shot if you haven't had one in the last 5 yrs. good luck!