An adventure game has a story, like a book or a movie. You go to interesting places, but there is little or no actual fighting. You solve puzzles and figure things out to progress in the game.
One common puzzle is to pick up items and then use them later in unexpected ways.
You can get great games here and the demos are free:
You can also buy the games used at Amazon.com
You can also go to bigfishgames.com and click on adventure. You can see a preview of the game there. You can download one hour of the game for free! And you can download the whole game for a third of the regular price.You can also get great games mostly for free here http://www.adventuregamestudio.co.uk/site/games/