Useful Links

How to Read Resistor Colour Codes
www.allaboutcircuits.com/tools/resistor-color-code-calculator/

The Theory Behind LEDs & Resistors
www.evilmadscientist.com/2012/resistors-for-leds/

Where Do I Put the Resistor? Before or After the LED?
forum.allaboutcircuits.com/threads/resistors-to-pos-or-neg/