Patrick Martin said:Man, you're the one who needs to tell me
what does stalker mean?
what is "the Zone"?
why did they go into the Zone?
what were those little coils they were throwing?
what does the police force represent?
what’s the deal with the black dog?
what is the significance of the daughter in the whole story?
I'll try to give you a really broad, simplified breakdown:
A stalker is his profession—a guide through the Zone—which is obviously illegal since the Zone is off-limits.
The Zone is a radiation-contaminated area, a place where aliens once landed (if we're going by the simple explanation at the start of the film or from the book).
People enter the Zone to visit a mythical location where they might have all their wishes granted, or perhaps seek some kind of personal redemption—assuming such a place even exists, which might just be a figment of the stalker's imagination. Remember how he talks about how nobody believes in anything anymore? Even those two guys don't. One was looking for artistic inspiration—really, an escape from the emptiness of his own life. The other carried a bomb to destroy the site because it might defy established scientific laws; he claimed it was out of scientific curiosity, but he actually just wanted to protect the rigid scientific system he lives within.
Those coils are essentially lures for deadly traps—they exist in the novel, but in the film, Andrei Tarkovsky places them on a spiritual level, or rather, within the stalker's own psyche.
The police guard the Zone—or rather, they prevent anyone from reaching a place that could have the aforementioned implications. It's all about maintaining the status quo and the spirit of the times.
The black dog is the only living creature (aside from plants) we see in the Zone, and to me, it represents nothing more than a projection of the stalker's imagination while he lies there watching that beautiful scene of the dog arriving. He felt closer to that dog than he ever did to those two men.
The daughter represents indestructible life; despite being irradiated and mutated into a telekinetic girl, she continues to live. She wears an oblek—that headpiece that looks like traditional American folk attire—and knowing how deeply Andrei Tarkovsky understood the concept of his homeland, the implications are endless.
This is all very simplified and rushed—there are countless lines in this film that could be the subject of entire essays.