Welcome to the 22nd century. In the game of Decker, you are a hacker who specializes in breaking into corporate computer systems, for which you are handsomely paid. Of course, these corporations don't idly sit by and allow you free run of their systems. The systems are guarded by Intrusion Countermeasure programs (ICE), which attempt to kick you out of the system, or possibly even kill you. 

The basic equipment of a Decker is the cyberdeck. This wonderful piece of hardware plugs directly into your brain in order to allow you experience the full virtual reality world of the matrix. While in the matrix, you use programs to attempt to bypass the security measures of the corporate systems, or to crash them if all else fails.

You start out unskilled, unknown, and underequipped, but as you gain experience, you will increase your skills, hardware, and reputation in order to combat more difficult and dangerous systems. That is, if you don't get your brain fried in the process.