It's a tricky subject.
Your altimeter calculates your current altitude with pitot-static air pressure sensors located on the aircraft's fuselage.
Normally, the way to perform an approach at any airport is to consult the ATC (or carrier) to get the proper barometric pressure setting. This way, you know that the altimeter will give you a reliable reading since the altitude you see on the HUD in BARO mode will always be correct.
However, in the tutorial I didn't bother with the barometric setting. 29.92 inches of Mercury (Hg) (or 1013,2075 HPa) is what we call the "Standard Pressure", which is a reference pressure used above the "Transition Altitude", which is yet another altitude reference as explained by Jak525. Instead, I used the Radar Altimeter mode in the groove since in that particular situation it gave a more accurate reading. You could've totally landed with the Barometric mode, but for that you absolutely need to get the right Barometric Pressure Setting from the Carrier Controller. Otherwise, fly the ball and forget about the Baro Altitude reading.
The Radar Altimeter mode has the advantage of being more accurate when flying straight, but the reading gets completely wrong when performing bank manoeuvers since the radar altimeter sends radar beams perpendicular to your fuselage, which is problematic when the wings are not level. Performing approaches over uneven terrain gives erratic readings as well.