Section header fields are not true fields, because they do not store any data.  Section header fields simply add a header to the auto-generated "generic layout" of a form.  Section header fields have very few settings.  Even most of the common settings are missing.  On the main edit page there are only the name, label, hint, grouping and custom lookup properties.  On the advanced tab only a simplified locking and hiding setting, and style class are available.  The permission tab, however, is unchanged.  You may be wondering why the permissions and locking an hiding settings are available at all:  It is simply to make the header go away when surrounding fields disappear, so you don't end up with a bunch of meaningless whitespace in your layout.

Format/Setting	Description
Name, Label, Hint	The name, label and hint fields determine exactly how the section header will appear in the generic layout.  A header spans the full width of the layout.  From top to bottom a header consists of: 12 pixels vertical of whitespace; the label (or name if no label is entered) in a large, bold font; a rule line; the hint below the line in an italic font; and finally 12 more pixels of vertical whitespace.  If the label contains only a space, it will be omitted.  The hint, if empty, will also be omitted.  If both the hint and label are omitted, then the header becomes simply a rule line with whitespace around it.  Customizing: The header is built using a few generic style classes in addition to any custom class defined on the advanced tab.  Many organizations choose to customize the look of headers by modifying these standard classes in the organization's style settings.
Grouping	Grouping can be disabled ("Standard Header") or enabled ("Auto-Collapse Header").  If enabled, a plus/minus box is added to the beginning of the header's label.  Clicking anywhere on the header's label row will show/hide the fields within the group.  When the page is loaded, the header's group will be collapsed unless it contains at least one field that is editable by the currently logged in user and not blank/empty.  Fields may be non-editable due to permissions, field locking/hiding settings, or other issues too rare and complex to be usefully described here. Grouping + Hiding When a grouping header is hidden either by permissions or by locking-and-hiding settings, it hides its entire group.  If the grouped header is hidden, then all of the members of the group will also be hidden.  This can cause very strange results if there are nested groups of different field types.  The nested grouping field will be hidden by the header group, but the nested group may not hide its grouped fields.