Locked out of MacBook

If you are referring to the following screen:

Then you need to enter the PIN that you set up in Find My when you remotely locked this notebook.

If you can't remember that passcode, you have three options:

• Sign in to iCloud.com/find, then select your Mac from the Devices menu. Select Unlock and follow the steps to verify your identity.
• Unlock your Mac from your iPhone, iPad, iPod touch, or Apple Watch using your device passcode.
• Take your Mac to an Apple Authorized Service Provider along with your proof of purchase.

Ref: If your Mac is lost or stolen - Apple Support