Inside screen of my touch phone is cracked. Which needs replacing: the LCD screen or digitizer?

I have a Samsung Solstice. It was thrown and the inside is cracked. The outside screen doesn't have any damage to it. I can't see ANYTHING; only lights and the crack. The touch screen still works; when I touch around randomly, the phone vibrates. Can't really get the phone service to repair it without it costing the same amount as a new phone, so I want to replace the part and repair it. I'm not sure which piece to replace though: the LCD screen or the digitizer? I'm not really sure what the difference between the two is. I really appreciate any answers!