Don’t know how to make outgoing calls

1.

Do you have a SIM card?

Put your SIM card in the phone.

Is your SIM card is activated?

If you don't have a SIM card, look for / visit a carrier, take a subscription, postpaid or prepaid card.

Check whether the SIM card is suitable for your iPhone.

Hopefully you have an carrier unlocked iPhone.

2.

Try to remove and reinsert the SIM card.

If it doesn't help contact your carrier, maybe the SIM card is damaged, ask for a replaced (new) card. Normally it is free.

Also ask to check if the SIM tray is bent, as even a tiny misalignment can cause the SIM card to not fully connect with the internal contacts in your iPhone.

See also this Apple article: How to unlock your iPhone for use with a different carrier

How to unlock your iPhone for use with a different carrier - Apple Support

• Apple can't unlock your iPhone for use with a different carrier. Only your carrier can unlock your iPhone.

You need to contact your Carrier.

Or do you need the PUK code?, See this Apple article: Use a SIM PIN for your iPhone or iPad

Use a SIM PIN for your iPhone or iPad - Apple Support

See also ⤵️

If you can't make or receive calls on your iPhone

If you can't make or receive calls on your iPhone - Apple Support

If you can't send or receive messages on your iPhone, iPad, or iPod touch

If you can't send or receive messages on your iPhone or iPad - Apple Support