Trouble with SQL Server authentication in SQL Server 2012 I am working with a SQL Server 2012 database. I am able to log into the server using Windows authentication. Although I have the SQL Server authentication username and password which is provided to me by the team, but authentication fails.

Is there anyway to find the password for the username : sa. Also, how to create new username and password without affecting the existing sa username.
New accounts with system administrator access can be created by other equivalent accounts but there is no way to reverse engineer the password for an existing account. You should also verify that the SQL Server you're connecting to allows for mixed authentication (Windows and SQL Server).

This StackOverflow question describes how to access authentication via SQL Server Management Studio (https://stackoverflow.com/questions/1393654/how-to-change-from-sql-server-windows-mode-to-mixed-modesql-server-2008)