How to create sql server authentication in server 2016

open microsoft sql server management studio 2016
connect sql server as a with windows authentication
select properties of sql server - security - from the server authentication - select 'sql server and windows authentication mode' - click ok

go to security - logins - here you can find sa
right click properties of sa -

you can change the secret password then click ok

again go to properties of sa - select status - turn login as 'enable'

disconnect the server

go to sql server manager

restart the sql server as well sql express

then get back the management studio and connect with sql authentication by using sa credential