Design Manager is a feature in SharePoint 2013 that makes it easier to create a fully customized, pixel-perfect design while using the web-design tools that you’re already familiar with. Design Manager is a publishing feature that is available in publishing sites in both SharePoint Server 2013 and Office 365. You can also use Design Manager to brand the public-facing website in Office 365.
Below article is focused on Enable Design manager in SharePoint and Open Design Manager in SharePoint.
You can refer the MSDN article on Overview of Design Manager in SharePoint 2013 for further details.
Enable Design Manager in SharePoint
Site Collection Features
Open Design Manager in SharePoint
You are here. It’s the Design manager Landing Page
What’s new with SharePoint 2013 site development: http://msdn.microsoft.com/en-us/library/jj163942(office.15).aspx
Overview of the SharePoint 2013 page model: http://msdn.microsoft.com/en-us/library/jj191506(v=office.15).aspx
How to: Convert an HTML file into a master page in SharePoint 2013: http://msdn.microsoft.com/en-us/library/jj822370(v=office.15).aspx
How to: Create a page layout in SharePoint 2013: http://msdn.microsoft.com/en-us/library/jj822368(v=office.15).aspx
What’s new in Branding ? http://edithzor.wordpress.com/2012/11/22/whats-new-in-branding/
Intro to SharePoint 2013 Design Manager: http://sharepointbrian.com/2012/07/intro-to-sharepoint-2013-design-manager/
Using Dreamweaver and Design Manager with SharePoint 2013: http://blogs.technet.com/b/speschka/archive/2012/07/27/using-dreamweaver-and-design-manager-with-sharepoint-2013.aspx