The Nameks are a peace-loving race that originated and dwell predominantly on the Planet Namek. The Nameks are all green with little antennae protruding their foreheads.
This is Dende. He's a
Namek.
The Nameks are very close to plants. They have the ability to reproduce asexually and they can regrow broken limbs. There are no male/female Nameks - they're all unisex (though they all act stereotypically of the male gender). Furthermore, also like plants, Nameks don't need to eat anything; they survive just on water. They are also a relatively powerful species and can attain a high power if trained hard enough (though they're not near the level of Saiyans).
We first meet three members of the Namek race (though they're interconnected very tightly) on Earth without knowing they're Nameks (indeed, they themselves don't even know it). We find out about the Nameks when Vegeta and Nappa comment that Piccolo looks to be from the planet.
Nameks were the ones who created the dragon balls. Guru, the oldest of them, created the most powerful of the dragon balls whereas Kami, the Earth's caretaker, created the Earth's dragon balls.
This is Guru. By golly, he's a Namek too!
Planet Namek itself is a very lush planet that was devastated by atmospheric changes. Guru was one of the, if not the only, survivor. He single-handedly repopulated the planet of its people. He is guarded by a fiersome Namek warrior named Nail.
The Namek are very proud people, completely unwilling to betray their own kind. Frieza and Vegeta have to find this out the hard way when they have to kill so many of them because they wouldn't talk. One of the only Nameks to face Vegeta/Frieza's wrath and live to talk about it was the child Dende. Dende inherits Kami's place as the caretaker of the Earth.
Nameks even have the power to fuse with one another (though Saiyans can do this too). We learn this when Nail permanently fuses with Piccolo to increase Piccolo's power.