The ambient temperature display shows you the air temperature directly around your meat. This number can differ greatly from the display on your oven or grill (which take air temperature readings differently). The ambient temperature reading will give you a better understanding of what temperature your meat is actually being exposed to. Generally, for most baking purposes that are timed (example: 350f for 30 minutes) the ambient temperature will not play a significant role. When smoking or cooking to a specific temperature that isn't dependent on time, the ambient reading can help guide you more accurately.
Ensure the Smart Thermometer is fully inserted into the meat with no stainless steel showing, and centered as best as possible. The black ceramic top that remains exposed (where the ambient sensor resides) should not be in direct contact with any surface to give you a good reading. Do not cover the ambient sensor with aluminum foil.