Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is one of the snakiest movies I've seen that isn't an Indian or Asian snake-woman movie or a horror movie. There are plenty of real snakes, a gigantic fake snake, arrows made to look like snakes, and we see lots of snake images on props, sets, and costumes all from the same production designer who worked on Alien. There are so many snake things I'm just going to spoil the whole movie here.
When he is a boy, a band of men carrying snake standards kill Conan's parents and destroy his village and take him away to be a slave, making him push a giant grinding wheel for years until he looks like a guy who spends too much time at the gym using steroids. He is taken away to become a gladiator and then he's sent away to get martial arts training from the Mongols where they keep him in a cage and throw in a woman every once in a while to use him for stud service to "the finest stock" of women. He finally escapes and sets off to get revenge on the men of the snake cult who killed his parents.
Conan discovers that the cult is led by Thulsa Doom (James Earl Jones), the man who cut off his mother's head. Conan teams up with Subotai, an archer, and they travel from city to city looking for information about snake cults. They meet a thief, Valeria, and the three of them climb up the snake cult's huge tower decorated with giant snakes, then rapel down into a hugh snake pit where they find "the eye of the serpent" a huge jewel that is guarded by an enormous boa constrictor. Conan grabs the jewel, but his sweat wakes the sleeping snake. He cuts off its head with his sword just before a naked woman wearing only a diaper jumps into the snake pit as a human sacrifice.
The local king gives the three thieves a fortune in jewels to rescue his daughter from Doom. Conan and Valeria fall for each other. She wants to take the jewels and run off with Conan, but Conan is bent on revenge and goes off without her to hunt for Doom and his cult and to save the princess. He meets a wizard who helps him sneak into the cult, but he is discovered, tortured, and crucified to a tree. Before Conan is left on the tree to die, Doom tells him he's most upset that Conan killed his snake. We see Doom's henchman and the princess and other cult priests all holding snakes and Doom also has a pile of Anacondas on top of a fountain.
Valeria and Subotai rescue the dying crucified Conan and the wizard brings him back to life. Then they paint themselves up like a heavy metal band and sneak into the cult temple through the back door where they see a huge kitchen cooking up human bodies into a green soup full of hands and heads that is fed to a bunch of stoned-out people at an orgy presided over by Doom, who knows how to party. We see Doom's blue eyes change into snake eyes, then he changes completely into a huge boa constrictor and crawls into a hole.
See video of Thulsa Doom's transformation Here.
The three capture the princess and kill everybody else, but as they are riding away, Doom turns one of his snakes into an arrow and shoots it at Valeria, killing her.
The three guys then booby trap the wizard's surroundings and wait there for the battle to come. After all his men are dead, Doom goes back to his temple so Conan goes back and kills him and burns down the temple. All the cultists put out their torches and go home and the narrator tells us that Conan goes on to fight many more battles and becomes a king.
Even though the movie was made in Spain, all of the live snakes we see are Boa Constrictors and Anacondas, all from the Americas. The credits list a "Snake Trainer" and a "Serpents Expert" even though none of the snakes did anything except the fake ones. There's some trick photography used with the large boa constrictor to make it look enormous next to the Princess.