I don't know what is wrong with me. I just simple generated a file using build.reduxframework.com and then added in my Wordpress theme. Then added the following line to functions.php
if(is_admin()){
require_once(get_template_directory().'/core/admin/admin-init.php');
}
Good thing is the demo stuff is showing up. Now my $opt_name is for_test. In my header.php I am adding the following code.
<h2><?php
global $for_test;
echo $for_test['textarea-example'];
?></h2>
PS: textarea-example is the id of the field which is already added in the files I downloaded. But I don't know why it is not fetching the value in it.