The Codex Entry on previous and next post links.

Use this for single post views to give your reader a way to chronologically “flip” through posts.

Be aware that next_post() and previous_post() were recently deprecated and the codex still lists these functions in some examples (they were replaced with next_post_link() and previous_post_link()). they will still work (for now).

Here is the most current way to navigate from post to post: