First, you will want to confirm that your device is able to inherently support an eSIM. The easiest way to do this is by confirming your device has an EID number. You can reference this article on how to confirm your device is eSIM compatible.
Next, the installation method will depend on your device:
iOS version 17.4 and above will see the 'Tap to Install eSIM' option as the first option.
Older versions will need to use the provided QR code to install their eSIM. Go to Settings > Mobile Service > Add eSIM > Use QR Code. If the QR code isn’t working, there is the option for a manual installation, which you can find instructions here.