Hello Aimee, there may be a few options depending on the displays condition.
Touch screens consist of a few different parts that can be replaced depending on the problem a user encounters. The two main parts are referred to as the digitizer and the LCD. The digitizer is the part that is responsible for sensing touch and sits in front of the LCD and is adhered to the bottom side of the top sheet of glass on the screen. The LCD is only responsible for displaying the image on the screen.
So if your screen is cracked and the touch function is not working at all or incorrectly but the it does display an image fine than you have the option of only replacing the digitizer. If the phone does not display a picture, or if the picture is distorted or displayed incorrectly than the LCD has been damaged and needs replaced.
You can usually purchase the display parts in numerous forms such as from individual pieces to the whole display assembly. Sometimes you can buy the front housing with the display already adhered in place. It all depends on the damage and how easy you want the repair to be and how much money to spend. Replacing the whole display unit as one is usually easier than replacing single parts of the display, but of course costs more. Hope this information is helpful to you.