Coolant level low and burning smell on 2013 Nissan Altima

Omg I'm freaking out can someone answer me before I stress myself out please lol

I took it to a mechanic and he put it on a diagnostic device and all the numbers were moving but the temperature which stayed at 194 so he informed me it suppose to go up or down according to the car heating up or cooling off which it wasn't so it's an indication of the thermostat going bad which is common in the Nissan's. He said by the thermostat not operating right causes the fluid to do something I forgot exactly what he said.