This is the 13419th most frequent Polish word.
palą
"Palą" means "they burn" or "they smoke," depending on context.
In this sentence, "palą" is used as the verb 'to burn' referring to the action of lighting a fire in the fireplace for heating purposes.
Oni palą w kominku, aby ogrzać dom.
They burn in the fireplace to heat the house.
Here, "palą" means 'smoke' and refers to the act of inhaling smoke from burning tobacco products, commonly cigarettes.
Palenie papierosów jest szkodliwe, ale niektórzy ludzie wciąż palą.
Smoking cigarettes is harmful, but some people still smoke.
In older usage, "palą" could mean 'to light up' a source of light, although this usage is largely outdated and has been replaced in modern language by terms like "włączać" ('to turn on').