1
If the person who gave you the PC, ask them if they can reser their Microsoft account password using the steps provided on this link, then try to log into the PC with the new password.
2
If they cannot reset their password, if that is a PC you have just been provided, and there is no other administrator account on the PC. then the best option to make that device your own, is to reset Windows while keeping nothing, if you have files on the PC, back them up first to ensure you do not loose any data.
Click the power button on the login screen.
Press the Shift Key and click Restart
Your PC will boot into the Windows Recovery Environment
Go to Troubleshoot - Advanced Options - Reset this PC
Choose to keep nothing
Then start the Reset