Thanks for posting your query at DoctorSpring.com. I can understand your concern.
The burning sensation during ejaculation can occur following infection. It can also happen due to prostatitis which is inflammation of the prostate gland. It would be best to see your doctor for the same who can examine you thoroughly.
The brown area seems to be a seborrheic keratosis which is like dead skin and is harmless. It can be burnt out by your doctor and removed.
Hope this helps, I would be glad to answer follow-ups.