In SharePoint 2013 the product group has worked really hard to change the way we consume SharePoint data, trying to make it easy to show relevant data.
One of the ways that this being done is the Search Web Parts, and one piece of that web part is the display Template. This template tells the web part two things and it does it’s work by creating an HTML page and a .js file.
So you ask how does this work? How do I create my template? This functionality is nestled under the Design Manager which means the heavy lifting will be done for you.
You would want to open/create the HTML file using any HTML editor then make it look the way you want and then save the file. Once it is saved Design manager will take it and create the .js file that SharePoint will use within the webparts. You can find more detailed steps for editing the html file in these articles http://msdn.microsoft.com/en-us/library/jj945138.aspx , http://technet.microsoft.com/en-us/library/jj944947.aspx .