Gangrene presents with skin changes (pale to black/blue/red), swelling, blisters, foul odor, severe pain (or numbness), and coldness, progressing from early signs like a red border to tissue death. 'Before' involves risk factors (poor circulation, diabetes) and early symptoms; 'after' treatment (surgery, antibiotics, debridement, sometimes amputation, oxygen therapy) aims to stop the spread, save the limb/life, and involves healing, potential reconstruction, or amputation, with recovery depending heavily on early intervention.