Resistors are a fundamental electronic component. They are used to limit current flowing through a circuit.
Resistors can have many different pre-defined values, measured in ohms. The bigger the value, the bigger the resistance, which means less electrons passing through. LEDs are a great way to learn about resistors, because you can clearly see the change in luminescence as you work up the values of resistors on your circuit.
The colored stripes in a resistor tell the resistance it has. You can follow a diagram to identify the resistor value.
To learn more about resistors, check the resistors tutorial at Sparkfun.