I'm sorry about the issue. Windows 10 uses Microsoft account (email address) login, so that it can sync data between computers (if you set up syncing), so that's why it uses the same password. If you need help with the password, you can reset it at the website https://account.live.com/ResetPassword.aspx
- If you'd like to use different passwords, then click on the Start button (which is the windows logo icon at the bottom left of the computer's screen), then click on Settings, then click on Accounts, then click on Your account on the left, then on the right, click on the option to Sign in with a local account instead (which from Microsoft account to local account.)
Please reply at the box below to continue troubleshooting. Thank you.