Each source list entry can be described as a primary, secondary or tertiary source. Once you have labeled sources, you can sort the list so that all of the primary sources are grouped together, followed by all of the secondary sources and then the tertiary sources.
On the Sources screen, mouse-over the area next to your citation in the "Tag" column and click the "+" icon that appears there (on an iPad, you may need to press once to display the "+" and then press again on the "+"). A menu appears with three choices: "Primary source," "Secondary source," and "Tertiary source."
When you select the appropriate source tag, a "P", "S", or "T" label will appear in the "Tag" column for that source.
To remove a tag, click the "P", "S", or "T" label and choose "Clear" in the menu.
To sort your citations into groups of primary, secondary, and tertiary sources, open the "Sort" menu at the top right of the Sources screen and select "Primary, secondary." The grouping is maintained when you export the source list via the Print/Export option.