There are alot of guides that teaches you how to hide fieldgroups with hook_form_alter function. However, those only works on in-built fieldgroups, such as Author Information.

Here's a very useful function that actually hides custom fieldgroups which you have created from the Field UI:

In a theme's node.tpl.php, we can easily render a field view using Drupal's render().

For example, we have a field name field_integer with the label My integer. To display the field in the node.tpl.php, we can just call it out using render($content['field_integer']);, which will display like the following (Assuming it is the default manage display setting for the field):

My integer:3 200

However, what if you want to render the field in your custom module? You won't be able to use render($content['field_name']).