Confusion: Why was I prompted for Password and How can I use it to log in?

Good morning:

I successfully installed SQL Server 2014 and I am able to access the System using Windows Authentication.

However, during the installation process I arrived at this screen below: (See screenshot).

I selected Mixed Mode, entered a password.

My question is, how do I also login using that password? When I go to SSMS and select SQL Authentication. I get error: 18456. Logging failed for user:Domain\Username.

The Server is already set to Mixed Mode and I have looked online for any information but nothing seem to work. I am also running the system as Administrator.

I created a password here: (Note: The username in the screenshot is a demo from Google images.)




Thanks for you help.