How to use option tree in my theme

hello all, I’m persian so sorry if I cant speak english as well as you.
I downloaded the plugind which named OptionTree
then I extracted the downloaded file into the template folder (wp-content/themes/my-theme)
now it’s active an I made some options but I dont know how to import these options into my theme
I just copied the code in the below into the index.php
the ID was logo_up for example:

<div class="header">
    <img src="<?php ot_get_option( $logo_up, $default ); ?>" />
</div>

but it doesnt show any changes…
what should I do?
how can I solve it??
Thanks alot