First step is to make an app in Facebook.
You should be an app developer to use Facebook comments in your website or blog or wherever you want.
To create a facebook app,
Go to below address.
If you are not yet a developer, register for a developer account.
Click on the button named "Create New app"
It will pop up a box. type your app name there. whatever it is. you can also name it as your blogs name.
Click next button, it will ask you to type captcha as Facebook requires that to prevent spamming.
Your app will be created and you will be taken to a new page where you can see basic settings of your app.
Display name will be the same name you typed.
Now , type blogspot.com,blogspot.[your country specified domain extension. example:if you are in India it will be blogspot.in].
You can complete the domain name list with country specified domain extensions as possible.
Next, you can see a field named sandbox mode.
If Sandbox mode enabled, only developers can use the app. so disable sandbox mode. for that check the radio button named "disabled"
Now, come down and click on website with Facebook login, and fill it with http://yourblogname.blogspot.com
Mine will be http://aslamise.blogspot.com
Now click on save
You have just made your Facebook app to use Facebook's plugins.
Get code for Facebook Comments
Cannot Find <body>
Ya it's your opening body tag. And you will find only one opening body tag in your template dear :) In Blogger, it will look like <body expr:class... just after the </head> tag.
Sorry I just got it :) I think you find it really hard with HTML. Let me explain it specifically. Add your code in a new line right after the line <body expr:class...>.
[Add Your Code Here]
Cannot Find <data:post.body/> in blogger template
Find ID Facebook
Now, the last step.
we have to hide the real blogger comments plugin from our blog.
for that, go to your blog's dashboard.
Settings -> Posts and comments ->
Under Comments Section, you can see an option named Comments Location
Note: Selecting Hide does not delete existing comments.
Then click save settings.
You have just replaced your blog's default comment system with Facebook's comment system.
Feel free to ask if you are experiencing any problem with the process. your comments are always welcome :)