The sibling tag allows you to traverse back and forth through the current page's entries using tag pairs and variables within the tag. It is intended for normal pages within the hierarchy and not listing entries. An example for listings follows the sibling tag below.
Linking to Page's Siblings
{exp:structure:siblings}
{prev}
<a href="{url}" title="{title}">Prev: {title}</a>
{/prev}
{next}
<a href="{url}" title="{title}">Next: {title}</a>
{/next}
{/exp:structure:siblings}
Linking to Listing Entry's Siblings
{exp:channel:next_entry channel="news"}
<a href="{structure:page_url_for:{entry_id}}">Previous Page</a>
{/exp:channel:next_entry}
{exp:channel:prev_entry channel="news"}
<a href="{structure:page_url_for:{entry_id}}">Next Page</a>
{/exp:channel:prev_entry}