Predator is a horror movie released in June 12, 1987 where the main character "Dutch", played by famous actor Arnold Schwarzenegger as he and his comrades are sent to guerrilla teritory in Central America on a mission to rescue hostages, but are encountered by an unknown creature known as The Predator.
In terms of horror films, Predator isn't necessarily horrifying, but the act of suspense is still like those you would see in other horror films at the time. Being one of 20th Century Fox's most popular movie franchises, Predator is still one of those films that could still be watched today without cringing at any poor special effects that were accessible at the time of its premire. Sometimes, Predator could be compared to 20th Century Fox's other movie franchise, Alien (which I still need to watch and I feel bad about myself for that).
If you're looking for a horror film to watch, but aren't sure which to start off with, I suggest you give Predator a chance if you're a bit too scared of common horror movie troupes in other films of the genre. If you're done with that there is sequel called Predator 2, but I personaly don't feel that it has the same appeal as the original. There is also a 2010 direct sequel to the first movie called Predators, but I felt that the movie was average at best when I first watched it in theaters and I still live by that opinion to this day.