Update Messed Up My Phone

Try clearing TouchWiz Home's cache (if you can get into the system settings still) then rebooting the phone. With any luck it's just that the launcher crashed and its settings haven't been lost, in which case your desktop might return to normal. If that isn't enough you could boot into recovery and clear the system cache (not the same thing as a factory reset) - that would be a long shot, but isn't a bad idea generally after an update.

If you it's the same after a reboot let us know. The next thing to try (if you can get into settings) would be to clear data for TouchWiz Home, which will erase your desktop setup but might help if the problem is an incompatibility between its current settings and a new version of the app.

If you can't get a desktop and app drawer back after that then assuming you don't want to do a factory reset the next thing I'd try is to install a different launcher. Go to play.google.com using a web browser on any computer, sign in to your google account, pick a launcher (e.g. Nova) and select "install". As long as your phone has an internet connection the launcher will install, and once it's done that press the "home" button - it should ask you which app you want to complete the action with, after which you can select the new launcher and you will have a desktop/app drawer again. Then you can set it up so you can use your phone, either sticking with the new launcher or at least giving you something you can use while we figure out what's wrong with the old one.

Do you have the status bar? If you have you can pull down the notification slide and get into settings that way (or you can on most phones via a little gear symbol there, and also my Samsung tablet. I don't have a S7 to check).

Otherwise try to "install a different launcher from the web" trick, or go into recovery and see whether clearing cache works (entering recovery will involve pressing some combination of keys while it reboots, can't remember what combination for a Samsung phone at the moment).

I don't know what you mean by "nothing is the same" in Settings. If it was a big change then some things might move, but key things like the Apps settings ("App Manager" Samsung rename it, on devices I've seen) should still be there something. So if you locate that find TouchWiz Home under "All" apps and clear its cache or maybe its data, then there's a chance that will fix your launcher problem.

It's possible you have a corrupt update, but more likely that there is some incompatibility between your existing data and the new software. This is why when people use custom ROMs they recommend a factory reset when moving to a different ROM or when the "same" ROM has a major update, but you don't want official Over The Air updates to reset the phone (will piss off a lot of customers!) so instead there is always a risk that there may be some incompatibility (since everyone has a different setup it's impossible to test every possibility).

If you do take it in I strongly recommend backing up everything important any way you can first, since it's quite likely they will do a reset while trying to fix something like this. And if that's difficult in your current state, that is why I proposed pushing an alternative launcher to the phone from the play store - that will give you desktops and app drawer again, which will make everything else you want to do much easier.

I meant (and said explicitly in post 2) the play website, from a computer. You can install apps to your phone from there. Launching an app would be a problem, but in the case of a launcher pressing the home button after it has installed would prompt it to ask you which launcher to use. So long as the phone has an internet connection you can do that.