The following functions will output links as described below.

If the post is not part of a series (as defined by the custom fields), the template tags will not display anything; so it’s safe to add these tags to your default template(s). If the plugin is deactivated, you will need to remove or comment out these tags.

Or you can use a construction such as this:
< ?php if (function_exists('next_in_series') ) {previous_in_series(); echo '&nbsp&nbsp'; next_in_series();} ?>
[djd]

< ?php previous_in_series(); ?>
displays a link to the previous post in the series, if there is one. If the current post is the first post in the series, this template tag will not display anything.

< ?php next_in_series(); ?>
displays a link to the next post in the series, if there is one. If the current post is the last post in the series, this template tag will not display anything.

< ?php all_in_series(); ?>
displays a list of links to each post in the series. The current post is not linked, to ensure the reader knows where in the series they are.

< ?php series_table_of_contents(); ?>
displays each post’s title as a clickable link to that post, as