My iPhone 7 front glass has cracked.

So in short term the actual screen that displays the picture and the glass are glued together, unless you have an expensive machine or amazing patience and the skill of not breaking the screen (which is very easy to break) you will need to buy a new screen. If you think the iFixit kit is expensive there are plenty of cheaper ones on eBay, but you might not get the same quality, if you do get that route either make sure it comes with the tools needed or you buy them separately. A YouTube tutorial or the iFixit one should help you out. Hope you get it fixed :)