There is an additional cost you can pay for called "Full Self Driving". This fee enables some new functionality like summon mode and the car changing lanes itself when you indicate a lane change. This fee is borderline fraud as people who leased early model 3 cars didn't receive anything close to the functionality described.
Autopilot is not ever active unless the driver enables it. You pull a stalk to turn on adaptive cruise control which only manages your speed and doesn't do any steering. Another pull of the stalk turns on autosteer, which is really just fairly fancy lanekeeping assist. You can buy a tesla and never use autopilot. There is some automatic emergency braking you can't disable, but that's true of nearly all new vehicles.