It's all about choices. Upon firing up Deus Ex, the first decision facing the player is whether to play the training module, which is separate from the game proper. If you do, you progress through a series of short instructional segments that introduce you to the principal game controls and to a variety of game actions such as opening doors, picking locks, jumping, crouching, swimming, picking up objects, shooting, handling small explosives, hiding from guards, healing, inventory, et al. A simple small training mission follows, requiring you to cross a large room that is divided by a water-filled channel and guarded by a security bot. This task serves as a very good preface to the actual game in that it can be accomplished in a number of very different ways.
Training also provides some basic information about various friends and opponents.
To begin the game proper, you must first select a difficulty level. There are four settings - Easy, Medium, Hard and Realistic. The game is one that offers plenty of challenges, so for the majority of players, one of the lower settings is probably appropriate to start with. Should your first choice be too easy or too difficult, you can change to suit your preference during the course of the game. Next up is the character generation phase, which is clearly designed to be quick and straightforward.