Error 18456 in sql server

In SQL Server's common issue in securities is login failed for user, Error 18456.
To resolve 18456 error, you have to change the Server Authentication mode "SQL Server and Windows Authentication mode".

In order to resolve the above issue through selecting "SQL Server and Windows Authentication mode", please refer to the following steps:
Here is the error #18456 getting while connecting to the server through "SA" login and password.

Workaround:  Step 1. Login to the Microsoft SQL Server Management Studio with Windows Authentication.

Step 2. In SQL Server Management Studio Object Explorer, right-click on the server, and then click Properties.

Step 3. Under the Server Properties, select "Security" page.

Step 4. Select the Server authentication as "SQL Server and Windows Authentication mode" and click Ok.

Step 5. After changing the server authentication mode from windows to SQL Server and Windows Authentication Mode, server needs to restart then only changes will effect.