In a first degree burn, e.g. by the sun the skin becomes red and sore, but no blisters occur. However, a second-degree burn. On large areas already a skin graft may be needed.
In a third degree burn destroys the skin. The wound area no longer responds to touch and pain stimuli.

Measures: extinguish if necessary. Watch out for power lines!
First time (at least 10 minutes) fresh water (approx. 20°C), the rest comes later. You can gently pour it, or dip. Refrigeration also helps against the pain.
Sterile cover with wet, cold compress.
A book with survival techniques of the SAS indicates tannin (boiled oak or beech bark) as suitable for cleaning burns.