Save to Central:
In Steve Stafford's RevitOpEd he has a brief but easy to follow explanation of what need to be done to create a Central File. The article is called Central File in "Four Easy Steps".
Save to Central options:
Nicholas lyadurai has a blog called Revitize - Another Revit Blog and one of his posts entitled "Save to Central differences"
Working in the Central file:
As we have all come to expect, Steve Stafford's RevitOpEd has an excellent article on when it is ok to work in the Central file. It's called, Working in the Central File - Breaking the Rule.
Central or Local File:
The last topic that I want to cover is a very good article again by Steve Stafford on determining whether a file is either a Central file or Local file. The article is called "Stand Alone? Central File? How can I tell?"
Steve has been blogging for awhile. He does a very good job and has numerous articles on the subject of the Central file.