Not much is known about these games. They were released in 1989 in two formats: the popular "multiscreen" format, and in the game watch format. They don't appear to have much connection with the real Zelda games, other than some official art and hastily-brewed stories.
Game & Watch Multiscreen Zelda
This game is not really a watch. It's more like one of those low-quality LCD games you can find in any drugstore, which also happens to tell the time. It is rectangular, and opens up (like a laptop). Both halves have a screen, but the bottom half, which you grasp, has the control buttons on it. Link starts at the bottom, and has to hack and slash his way past Stalfos to reach Zelda at the top and save her.
Game Watch Zelda
This was an actual watch made by Nelsonic, with a Zelda game built in. Maybe the watch was okay, but I hear that the game wasn't very fun to play. The format was really too small to do much with.
Some information taken from Videogames.com's History of Zelda