I can't log into my MacBook Air

You need your password login user name to sign in to your MacBook Air.

See the following Apple articles:

If you forgot your Mac login password -> https://support.apple.com/en-us/HT202860

Change the login password on Mac -> https://support.apple.com/en-gb/guide/mac-help/mchlp1550/mac

Reset your Mac login password -> https://support.apple.com/en-mn/guide/mac-help/mh35902/mac

If you can't reset your Mac login password -> https://support.apple.com/en-gb/HT212190

See also -> Ways to remember passwords on Mac

Ways to remember passwords on Mac – Apple Support (UK)

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You are sign in here .  .  .  with your Apple ID & Password.

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

See -> Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

See what already posted.

New MacBook Air-and have forgotten my password—I am locked out—how can I change the password?