A truss rod is an interior metal bar running the entire length of a guitar's neck. When tightened, it counteracts the tension created by the strings (the strings pull the neck forward; the truss rod pulls the neck backward). Proper use of the truss rod enables you to "balance" the tension on the neck and adjust the amount of bow to fit your playing style. The truss rod is fairly rugged, so you shouldn't worry about experimenting with different adjustments. Through practice, you will find that you can compensate for seasonal changes, different string gauges, different playing styles, and slightly worn frets simply by adjusting the truss rod.

Typically, a properly adjusted truss rod will leave a neck with a bit of forward relief. You can use your strings as a "straight edge" by pushing them down to both the 1st and 14th frets simultaneously.

Then the gap between the string and the 6th fret can be observed. A gap slightly thinner than a business card is about right. From this point, you can adjust to your own preference.