The problem is with the LCD layer of the screen and it's a physical problem. The screen is going to have to be replaced. Technologically ignorant or not, I wouldn't advise doing it yourself until you've replaced at least a few screens under supervision. If the phone is in otherwise good condition, pay a shop to have the screen replaced. (Your carrier's repair facility is the best place to go, even they may be a little more expensive than some independent, unless the indy shop has a good reputation. In either case, make sure that they're willing to copy off any information that's not already backed up. (Your emails are. Your texts might be - it depends on how you set the phone up. Apps you got from the Play Store are still on the Play Store and you can install them again. [The button will say "Installed", but just press it and the app will install. If you already paid for an app, you won't have to pay for it again.] Any other data? You should have anything important backed up anyway - what happens if the phone gets driven over, stolen or lost?)
Most shops do a factory reset before doing anything else, just to ensure that their employees don't steal your data. (Identity theft is easy if I have your phone and know how to unlock the lock screen.) If you and the shop owner or manager agree to not reset the phone (it's not necessary to reset the phone to replace the screen), you'll get back a phone with all your data on it. (That's one of the reasons I said "good reputation". I owned cellphone stores for years, and would have called the police myself if I found an employee copying anything from a customer's phone. And with some of our customers there was plenty of temptation - loads of really good porn, which the employees shouldn't have even seen, and were warned about looking where they had no business looking. And I only issued one warning per employee, and they knew it.)