A past participle is just a verb conjugation that describes something that is over and done: written, said, cooked, closed etc.
Ele está perdido? He's lost?)
Ela está cansada. (She's tired.)
O shopping é chamado Rio Sul. (The mall is called Rio Sul).
*The endings must take the gender of the subject:
A porta está aberta.
Ele está perdido.
Irregulars include:
Ele foi morto. (He was killed.)
A porta está aberta. (The door is opened.)
Está tudo feito. (Everything's done.)