Its basically just a plate of glass, with a little digitizer chip attached, and a cable with the homebutton attached. It sits on top of the lcd.
You can get three different parts AFAIK..
1: LCD, glass and digitizer. These cost anywhere from 130$ and up on eBay and Amazon, though you can get them even cheaper sometimes. This is to replace all the display parts, in case the LCD is also cracked or completely black.
2: Glass and digitizer. Is the lcd behind the glass fine? Then you only need to replace the glass. This one comes with a new digitizer chip, so you can just take your cracked glass out and put this in. It usually costs 50-100$
3: Glass. No digitizer. Only the front glass. The drawback is, that you have to user your solder, to get the digitizer off your old iPad, and then solder it to the new one. And switch the homebutton too. This is much harder than getting a front glass that comes with a new digitizer already mounted to it. But hey, if you already have a solder iron, and you're not scared off from watching the how-to videos, then it's a nobrainer. 30$-50$ and up, though you sometimes see it for 20$.
Ifixit also sells the parts you need, and are a lot less shady than some of the cheap