P = program auto exposure: Although Program is essentially an automatic mode in that the camera determines the shutter speed and aperture setting for the scene, you can adjust those parameters in tandem. On the T6 mode dial, Aperture priority is labeled as AV (aperture value), and Shutter priority is labeled as TV (time value).
Though the fully automatic modes are easy to use, you're better off getting to know - and using - what is often referred to as PASM (Program, Aperture priority, Shutter priority and Manual).