In order to make this plugin work, you will need facebook App Id and App secret for your application. The App Id and App secret can be found on facebook developer section from MyApp links.
If you have not registerd you site as an application on facebook, Please register your site as a new Application n facebook. You can create an app using the link http://www.facebook.com/developers/createapp.php
Once you have created the Application, make sure to configure it on facebook properly. Please make sure you have entered your site domain/address in the website tab, as shown below.
That will make it work for your site now. Please keep reading for a little more details.
Mapping BuddyPress xprofile fields to Facebook Data:-
You can map specific BuddyPress fields to facebook fields. That will enable you to fetch the data from user's facebook profile and use those details for use's BuddyPress Peofile.
The mapping option is available, just below the basic settings screen of the BuddyPress Facebook Connect+ plugin as shgown below
All the xprofile fields from every field group will be listed. You can check a field to update it using the facebook data. from the dropdown, you can select a facebook field whose data will be copied to this field.
The plugin allows you to localize the various string used in the plugin/plugin admin. Please use poedit to translate the po file. You can see the po file inside the buddypress-facebook-connect-plus/languages directory. Name the mo file to you_Local.mo ( eg. en_US.mo or nl_NL.mo)
Depending on your locale settings, The plugin will show appropriate version of facebook login wizard.
You can use shortcode to show the button anywhere you want.
[fb-login] your login text here[/fb-login]
Is there any way to use it in php code?
Yes, please use the following code
echo bpdev_get_fb_login_button("Your Login Text");