How does unpack works?

Hi, I'm trying to extract an binary file with unpack but I don't understand how it works... The F6FBB program makes the file... It is a hamradio program http://www.f6fbb.org/ This is the structure of 1 record in the file : struct inf_struct { char callsign[8]; /* Callsign */ char dummy1[64]; long lastmes; long connects; /* Number of connexions */ long hcon; long lastyap; int flags; int on_base; char nbl; char lang; long newbanner; int download; char free[20]; char thema; char nom[18]; char prenom[13]; char adres[61]; char ville[31]; char teld[13]; char telp[13]; char home[41]; char gra[7]; char priv[13]; char filtre[7]; char pass[13]; char zip[1]; } inf; /* 360 bytes = lenght of one record */ Can somebody help me? Regards, Vincent