Server is in single user mode

I have just purchase vps hosting on GoDaddy and installed sql server 2014 with Managerment Studio.
Today I got error like server is in single user mode. only one administrator can connect at this time on my website. Error comes for 2-3 minutes and gets resolved automatically.
What this error is? I am newbie and don't know most of the settings. Can anyone suggest me why it happened?

The error message indicate that someone else has made connection to SQL Server, due to which SQL Server is not letting you get in.
Here is how can you fix this issue: