The simplest way to connect to an SQL Server database is to drop down the server name drop down list (directly under the database icon) and select it from the list. Alternatively you can write the server and instance name.
Once selected there are two connection methods, Integrated Security and SQL Authentication.
Inetegrated security works by passing through your Windows Authentication. The connection to the SQL Server is made using the user name and password you used to log into your computer. This is the most secure way to connect to an MS SQL Server and is the reccomended approach.
Pressing the ellipse (three periods in a row) will allow for SQL Authentication. This allows you to supply a non-Windows/domain user name and password. Although not as secure, this is the standard way of attaching to many cloud/internet based SQL Server instances.