Temperature control is a mechanism that (currently) works via two main mechanisms on the DC-DC regulator board powering mods with the function, one, TCR curve input and two, electrical resistance pinging. Basically, depending on the wire, a TCR curve will either be already on the board's memory or in the DNA/Newer SX Boards case be uploaded through software like Escribe/SX-Q, some mods have a value system you can input but this doesn't work all that well. The TCR curve gives the board a sort of 'feel and sense' for the wire to put it in layman, then through electronic resistance pinging, the mod CONSTANTLY will ping the coils in the atomizer to detect the smallest of small changes in resistance. So as your coil heats up, it resists current more, so its resistance (ohms) will climb, as it climbs, the board detects this and will modify the wattage output (usually by bucking it down) to maintain the input temperature. TCR curves give the board an idea of the wire, then pinging the resistance as the coil heats up does the rest. Most mods have a preheat wattage, which will be the power delivered for the first second or so, this allows the coils to get close to the desired temperature, then the mod detects the climbing resistance and cuts the wattage down to maintain a temperature around your setting. This technology can be VERY hit and miss depending on which board is in your mod, your settings and the wire used.
Temperature control is a POOR term for the technology as it is right now, temperature LIMITING is a better one. Basically the board will limit your coil builds to whatever temperature you set. Some wires have a more stagnant resistance like Kanthal, these are very poor TC wires. Some like Ni200 (Nickel 200), Titanium G1, NiFe-30 (Nickel Iron 30) and 430 Grade Stainless Steel have a resistance that changes drastically as the wire becomes heated. These low resistance wires climb in resistance as the coil heats, through TCR curves and pings the mod monitors and corrects the wattage to try and stay at that temperature. This can be very accurate or piss poor accurate depending on the board and settings used. The idea is to reduce dry hits when the wicks run out of juice by keeping the temperature below or just at the burning temperature of cotton. This can lead to longer hits, more hits out of a wick/build, less dry hits, a cooler vape and to some better flavor.