How to Set Facebook Comment Box:
1) Its very easy to set Facebook Comment Box in your site Go to the below link
or click here
2) You should have to login as a facebook apps developer, So only you can access it.
3) You can see a box as given below in the link.
Fill the box according to your Site detail and set the settings as you want
4) After that click on Get Code button, You will get Two Tabs
i) Copy the First tab code and paste it intag of your site. You need to have to go to Theme codes of your site to paste it. (Search fortag and paste below it)
ii) Paste the Second code as a Widget as where you want to set it in your Site.
5) Then Save your arrangements in your site, Now there will be comment box in your site
You are done, Now you can have a good Interaction of your Site Viewers through Commenting.