Use an iPhone or iPad to connect to the internet
Your Mac can use the personal hotspot on your iPhone or iPad (cellular model) to connect to the internet when your Mac and the device are within range of each other.
Before you try to connect, make sure your iOS or iPadOS device has its personal hotspot turned on (to check, go to Settings > Personal Hotspot on your device).
Note: This feature may not be available with all carriers. Additional fees may apply. Contact your carrier for more information.
Connect using Wi-Fi
Make sure your iOS or iPadOS device and your Mac are signed into iCloud with the same Apple ID.
On your Mac, click the Wi-Fi status icon
in the menu bar, then choose your iPhone or iPad.After you connect to the personal hotspot on your iPhone or iPad, you can use the Wi-Fi status menu to check your device’s battery status and the strength of its cellular signal.
When you’re not using using the hotspot, your devices automatically disconnect to save battery life.
Connect using USB
Connect your iPhone or iPad to your Mac with the USB cable that came with your device.
If you see an alert on your iPhone or iPad that says “Trust This Computer?” tap Trust.
To view the USB connection status on your Mac, choose Apple menu 
> System Preferences, click Network, then select iPhone USB in the list on the left. You can also select or deselect the “Disable unless needed” checkbox.