Can someone explain "access arguments" in Drupal?

in /admin/user/permissions you will see lots of access options. they come from drupal modules, and lets the site administrator distribute specific permissions to user roles (drupal provides 'anonymous' and 'registered' roles by default). modules declare them through hook_perm and they are as easy to use as:

function mymodulename_perm {
return array('use custom feature', 'use the other custom feature');
}

and they will show up there, ready to be used. now, in any function of yours, you can check for user access through user_access which is just as easy to use:

if (user_access('use custom feature')) {
  //do something
}