i want to know about sim lock

What exactly do you want to know?

It is normal for a carrier to lock the SIM card that is installed on the iPhone so the phone cannot be used to connect with other carriers until the original carrier unlocks the SIM card.

If you are thinking of switching carriers, you will need to get your current carrier to unlock the SIM card before you will be able to connect to the new carrier.

Depending on the original sales agreement, the original carrier may be under no obligation to unlock the SIM card.

Do you know who the carrier is? If you are using the phone now, you are sending a payment each month to the carrier.

Tap Settings > General > About

Scroll down to see the Network and Carrier

See this article.

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

Only the original cellular carrier may unlock the iPhone if they choose to do so.