The 18-55mm lens in the first (cheapest) kit is a "standard zoom", an equivalent to the classic 28-80mm zoom for film SLRs. It's versatile range being wide enough at 18mm for most landscape and interior shots, and long enough at 55mm to shoot tight portraits (head and shoulders) whilst being a comfortable distance from your subject (which also avoids any weird perspective effects).
The 18-135 is encroaching on "superzoom" territory, going from the same wide angle 18mm but all the way to 135mm, allowing you to shoot subjects that are two and a half times as far away as the 18-55mm lens. This extra range adds to the complexity of the lens design accounting for the difference in price.
Whether this is worth the additional cost is up to you. In general it is better to get different lenses for different purposes rather than a single jack of all trades lens, however if you want to travel light, or are a casual photographer and don't want to change lenses all the time it may be the right lens for you.
There are several tools online (such as this one, select "DX" as the format and compare 18mm, 55mm and 135mm) to help visualise the results of different focal lengths.