Please download the latest owner's manual from MyTesla and look for AutoSteer in the ToC. In my copy it's on page 74.
As others said, definitely take the time to read over the 5 or so pages related to this topic. In addition to being aware of the limitations of the system, definitely be wary of:
- Who is in control. Blue is the magic autopilot color. Similar to TACC, blue steering wheel = AP engaged, gray steering wheel = AP available but disabled. You will hear chimes telling you when AP is activated, and the opposite chime when control is disengaged. So far, one of the two known AP-related accidents had to do with confusion regarding who is in control.
- What the car thinks is going on: You're probably already familiar with how the instrument cluster draws realtime diagrams of what the car is seeing. AP augments this further by drawing in blue what it is obeying. A blue lane line on either side means that AP recognizes the lanes and is using them as the primary Autosteer reference. In this case you should monitor whether or not you agree with how it feels your car is centered between the lanes. A blue car ahead means that AP does not trust the lane boundaries and is exactly following what the car in front of you is doing. In this case, you should carefully monitor what the car in front of you is doing, and be ready to take over if he does something you don't want to do, such as move to a different lane that isn't safe for you, drive off the shoulder, take an exit on the highway, etc.
Autopilot relieves you of the mundane duties of driving and turns you into a supervisor / driving instructor of your own car. You can either choose to use this ability to make your driving safer (by taking advantage of being able to look around you more and gain more big-picture awareness of potential problems around you), or mitigate risky behavior (e.g. if you *really* have to mess with your phone / touchscreen, fidget with a child in the back seat, etc, it's safer to do so with AP engaged than to let go of the wheel altogether in a traditional car)....
Just be aware that it isn't a self-driving car, and I've seen reports of at least 2 accidents when Autopilot was engaged or allegedly engaged. You are still responsible for everything that happens regardless of AP