How to display fields horizontally in a node?
The default behavior of Drupal's field display is to wrap the content in DIVs, which are displayed as block-level elements by default, hence, one per line.

There are a number of different ways to solve for your display needs.

As Sidharth mentioned, displaying fields can be done via custom CSS. Typically you'd want to create a custom node.tpl.php for your theme and apply your CSS rules to those elements in your template. 

Another solution, if you're not looking for custom templates for different node types, is the Field Group Inline module.