You're on WiFi. The signal looks fine. But nothing loads.
What's going on?
Before your browser can load a website, it needs to consult a digital phonebook. We call that 'digital phonebook' DNS, or Domain Name System.
Your computer doesn't understand words like google.com. It only understands numbers (IP addresses). So it asks the DNS service:
"Hey, what's the number for google.com?"
If the DNS service is down, that lookup fails.
The internet is like a layered cake. Each layer handles a different job.
If one layer goes down (DNS) but the others work fine, then you would still be able to use Google's service, but only if you knew their IP address by heart.