When in the scope of a post, you can call the next or previous post helper, which performs a query against the API to fetch the next or previous post in accordance with the chronological order of the site. Inside of the opening and closing tags of the {{#next_post}}{{/next_post}} or {{#prev_post}}{{/prev-post}} helper, the normal helpers for outputting posts will work, but will output the details of the post that was fetched from the API, rather than the original post. 
{{#post}}
	{{#prev_post}}
		<a href="{{url}}">{{title}}</a>
	{{/prev_post}}

	{{#next_post}}
		<a href="{{url}}">{{title}}</a>
	{{/next_post}}
{{/post}}
You can also scope where to pull the previous and next posts from using the in parameter 
{{#post}}
	{{#prev_post in="primary_tag"}}
		<a href="{{url}}">{{title}}</a>
	{{/prev_post}}

	{{#next_post in="primary_tag"}}
		<a href="{{url}}">{{title}}</a>
	{{/next_post}}
{{/post}}