The Edit Person sources view provides a list of all source citations attached to the person, their families, events, or names.  When you highlight a row, the source and citation will be displayed on the right where they can be directly edited.

Above the list is a drop list where you can filter the list down to a single item (general, name, fact, etc.).  A search box lets you filter the list by the source name or citation name.

You can add source citations to any record, depending on which filter you have chosen.  For example, if you have filtered to show the citations for the person's birth, then clicking the + button will let you add a new citation to that birth.  If you select Add when the list is not filtered, the citation will be added as a general citation for the person.

You are also able to delete, memorize, or paste citations using the icons on the toolbar.

If you have the list filtered down (general, a fact, a name, or a family), you can click the up/down arrow button to rearrange the citations for that particular record.