Drive series of 1W led with mosfet
In general, high power leds can't be "driven" with a constant voltage and series resistor like one would do with signal leds, because the power dissipation in the resistor will be rather high. Consider 500mA through 50 Ohm will result in 25W being dissipated.

Driving an led usually refers to providing the led with a constant current, which typically requires some kind of closed-loop regulation.

In your case (assuming 6 leds @3.7V,500mA) you would need 3.6 Ohms as series resistance (voltage overhead is 24V-6×3.7V=1.8V, R=1.8V/0.5A=3.6Ohm). The power dissipation would be 1.8W, which is still pretty much.