“Unfortunately, App has stopped” is Android telling you the app died, not that your phone is broken. Here is how to narrow the cause down in a few minutes and fix it without wiping anything.
An app that refuses to update is not one problem — it is about seven, and they have different fixes. This walks through them in order, and explains the one case where reinstalling really is the only answer.
Everything else in the house is online, but your phone insists the Wi-Fi has no internet. Android is running a specific test behind that message — and once you know what the test is, the fix is usually one setting away.
The Play Store says “Download pending” and nothing happens. The message is not an error — it is a queue. Here is how to find out what is holding the queue up, and nine fixes in the order worth trying them.