The type guitar strings you use can make a huge difference in your playing. There are several variables to consider: size and material. Acoustic guitar strings come in a variety of materials including bronze, phospher bronze, brass, polymor and steel. Classical guitars use nylon strings which can sometimes be made from other materials as well. Electric guitar strings are mainly made from steel or nickel.
String gauges can also affect sound and playability. Lighter gauges allow more bends, play faster, but also break easier and produce less sustain. Heavier strings produce more volume and sustain and stay in tune easier, but may be harder to play. There are various sizes from extra light to extra heavy. Read more about choosing guitar strings here.