burn: be on fire.
Help! My house is burning!

catch fire: start burning.
Help! My house has caught fire!

flicker: burn unsteadily.
The candle flickered in the wind.

smoulder: burn slowly without flames.
The cigarette smouldered in the ashtray.

flare: burn brightly but unsteadily or briefly.
The match flared in the darkness.

flame: burn in flames.
The fire flamed up when he put oil on it.

burst into flames: suddenly start to burn very strongly.
The oil truck crashed and burst into flames.

blaze: burn brightly and fiercely.
When the firemen arrived, the whole house was blazing.

rage: burn very strongly.
The fire raged through the forest for days.

incinerate: burn something completely to ashes.
All the infected clothes were incinerated.

smoke: give out smoke.
The fireplace smokes too much.

brand: burn a mark on something.
Cattle are usually brandred on big farms.

scorch: burn or discolour a surface by dry heat.
She scorched my shirt when she was ironing it.

sear: burn something with a sudden powerful heat.
The heat seared his skin.

singe: burn the surface of something slightly.
The flames had singed his hair.

char: burn something so that its outside becomes black.
Roast the peppers until the skin begins to char.

cremate: burn the body of a dead person at a funeral ceremony.
Before a dead person is cremated, an authorization must be obtained.