Windows 10 allows you to sign in either with a traditional user name and password, or log in with a 4 digit PIN number instead.
This page opens:
Click the Accounts option shown above:
As shown, click "Sign in options" and then select "Change" in the "PIN" section. When you click that you can set a 4 digit pin as your log in. Once you have set that up you can log in with the PIN or select the password option on the log in screen and sign in with that instead. There is no loss of security by selecting this option and it certainly is more convenient.
The key thing to remember is that your password is still your login password, the PIN is just set up as an alias to that. So when you enter the PIN as long as you get it right, Windows still logs you in with your password automatically.
This completes this how to.