The interface might give you a first person view of the world, a third person view, or a god's-eye view. Either way, the character is your puppet. Some games will allow or require you to play several characters. Distilled to its basest essence, an adventure game is a puzzle to be solved. The big puzzle usually contains many smaller puzzles.
Many adventure games contain more than just riddles and logic and assembling pieces of a puzzle.
They might also include arcade sequences, like shooting down invading aliens, and synchronous combative duels, like a game of chess. A game challenge is any such obstacle that the player must overcome to complete the game. Much of the creativity of an adventure game consists of inventing new types of challenges. Your character is usually not the only active being in the world. Actors are other characters that are controlled by the computer.