If your carrier assigns you an eSIM when you purchase your plan, it will activate automatically when you set up your iPhone.
If an eSIM isn't assigned to you when you purchase your iPhone,
you can transfer your phone number from your current iPhone to your new one using eSIM Quick Transfer
Make sure your current iPhone is nearby and follow the prompts
on your screen to begin setting up your new iPhone.
When the Set Up Cellular screen appears,
tap the line you want to transfer.
additional lines can be added after your phone is set up.
Also, if your current iPhone has a physical SIM card, you'll be able to convert it to an eSIM.
Then tap Continue and follow the prompts on your current iPhone
and your new iPhone until cellular setup is complete.
When you finish setting up your iPhone,
your old physical SIM card will no longer work,
and your eSIM will be ready to use.
Other Method
Depending on your carrier, you might have to activate your eSIM using other methods,
Follow the prompts to begin setting up your iPhone.
When it's time to activate your eSIM, you can choose Use QR Code and scan the code.
Then just follow the prompts until your eSIM activates.
You can install the new plan or set up an additional line, in Settings after your iPhone is set up.
You might get a notification from your carrier, to activate your plan, or you can open Settings.
From Settings, tap Cellular, and then tap Set Up Cellular.
This button might say "Add eSIM" if you're setting up additional lines.
Follow the instructions to activate your eSIM, or you might have to scan a QR code.
Once you've completed the steps, your eSIM will be active and ready for use.