You can create a new source from scratch or from a template.
Go to the Family tab on the People workspace
In the editing panel, click the Source citation button next to the fact you want to add the source to. (example birth)
Choose Add New Source Citation from the drop down list.
When the panel comes up click on NEW.
The template panel will come up next.
type a key word in the source template area (example birth).
A bunch of different types of templates will appear. Choose the one that is the most helpful.
Fill in the information the way you want and then you will have a permanent source citation for that particular kind of information.
It is kind of slow going the first time you do it, but it really is quick and easy once you get the hand of it.