Ports are a way of sorting requests sent to the same physical device into different services. If a single device is providing three different services, you want to send your request to the right service on the device. For example, maybe your device has a website, a piece of accounting software, and an online video game running on it. If it weren’t for ports, you’d need three different devices to run those three different programs. But with ports, as long as I know what port the service I want is on, I can send my request to the right service on that device.
If you have limited money to buy devices but you want to make a lot of different apps, ports are important. Ports are also important if you’re a business like Google that provides lots of different services.