LEDs come in 3 basic wiring styles: radial lead, axial lead, and surface mount. Through-holes use only axial and radial. Radial means both leads come off the same side (actually the bottom). Axial means each lead comes off a separate side. Usually, the long lead is the positive, the short lead negative. If the LED has a flat on one side, that's the negative lead. If you can see into the LED, the large part is the negative, the small part the positive. If you're connecting single LEDs to the power source, it doesn't matter which lead you attach the resistor to.
Here's what I mean by a single LED to the power supply.
Here are 2 LEDs is series.
Here are 2 LEDs in parallel. (not the clearest diagram, but it is accurate)
Axial lead
Radial lead
And for all who know what anode and cathode are, I'm trying to keep this in simple non-technical terms where ever possible.
Here's where things get technical. LEDs are constant voltage devices. The means if you supply too much voltage (even a little too much) the current used by the LED increases significantly and POOF - no more LED. However, it also means if the voltage is too low (even by a little bit), the LED will fail to operate. No damage, just no output. Each LED has a design current for maximum output (of light). These two factors, design voltage and design current, along with the supply voltage are used to determine the the value of the resistor. If the power supply voltage matches the LED's design voltage, NO RESISTOR is needed.
The whole point of the this is that a 2400 ohm resistor sounds awfully large. A typical LED connected to a 12 volt power supply would require a 500 ohm resistor.