For many people that simply cook a lot due to necessity, knives do not matter that much. For others of us, cooking is a passion, and so is food. We do not just eat to live. We embrace food and all it has to offer in all it's forms.  For those of us who are passionate, cooking tools are critical. One of the most important are knives, and the chefs knife is the most common used knife.
Essentially all knife sets include a chefs knife, regardless of the quality of the knives. Some of us develop pretty strong preferences as well as preferences on pots, plans, stoves and the like. Here is some information on chefs knives so that you can better understand them. Knowing a little before starting to look and shop can be extremely useful for those of us who grew up with mediocre at best consumer knives.
A chefs knife is an all purpose utility knife, and tends to have a broad and relatively heavy blade, as well as a great feel in the hand. The blades vary from perhaps 7 to 12 inches long, but 8 to 10 inches are the most common. Like all good knives, they need to be regularly sharpened, should not be placed in the dishwasher even if they claim they are dishwasher safe, and need to be treated well. If any manufacturer or salesperson tells you a certain brand or style of knives never need sharpening, they are either trying to sell you poor to mediocre knives that can never get sharp or are enormously misinformed.
There are two main styles of knives, German knives and Japanese knives. German knives are probably the ones you grew up with and include well known names like Wusthof and Henckels. They are typically built like tanks and sharp as well as strong. They are relatively heavy and big. The other style is Japanese, and popular brands include Global and Shun. Japanese knives are similar to Samurai swords with multiple layers of metal, amazingly sharp, but somewhat brittle. Comparing Germans style knives to Japanese style knives is like comparing a tank to a Porsche. They both have their uses.
Many cooks, both amateur and professional use a mixture of the two styles of knives. For example I have styles of chefs knives and use them both for different purposes.