Members Multisite User Roles Sync

SBI

Where is the settings page for this plugin?

There is none. You simply activate it and it will work right away.

Is there a function to add a role to a user programmatically?

Yes, there is. See this example code:

<?php
$members_mu_user_roles_sync = new Members_Mu_User_Roles_Sync();
$members_mu_user_roles_sync->add_role(
  $user_id, // user you want to add role to
  $roles = array(), // input array is needed
  $all_sites = TRUE
);
?>