@nijamutheen
You have it in plugin configuration in section Plugin setup.
If you want to place initiate chat button on specific place, you can use built-in function. This function has optional parameter $user_id that does not need to be used.
<?php if(function_exists('oc_chat_button')) { echo oc_chat_button(); } ?>
If you want to show circle with user status (online - green, offline - gray), you can use built-in function. This function has optional parameter $user_id that does not need to be used.
<?php if(function_exists('oc_user_status')) { echo oc_user_status(); } ?>
If you want to use it in different way, take a look on function oc_user_status how to retrieve if user is online or offline.