How to call one file functions in other files in custom module? I have created custom module in Drupal 7. 

I want to create one file and in this file I want to create all functions that I need to use in this module. I want to call these functions in .module file. So for this what file and how can I use these functions?
It's PHP, so you use require or include to include functions from other files.

Drupal's wrapper around those is module_load_include. Examples from the docs:

// Load node.admin.inc from the node module.
module_load_include('inc', 'node', 'node.admin');
// Load content_types.inc from the node module.
module_load_include('inc', 'node', 'content_types');


Only use this function inside another function, not in global scope. If you need to unconditionally depend on a separate file for a whole module, just use require_once or whatever makes most sense for your use case.