The Facebook Comments Atom allows visitors to a web page to leave comments through their Facebook accounts (to which they will have to be logged in independently). These comments will be displayed on the Facebook Comments Atom, as configured below, as well as on the Facebook account of the commenting user.
The Atom will need to "understand" exactly which object is being commented on! This sounds simple - but ... as an example, News Items are displayed via a single Web Page. It is unlikely that the user wants to comment on the news Web Page itself, rather the News Article! So, whilst the Comments Atom is on the news Web Page, the Facebook Comments Atom will need to know that the Comment refers to the News Article ObjectID.
This is configured ON THE WEB PAGE, which is explained in more detail in a separate Help Resource. However, it is worth highlighting here that the Web Page that is displaying the News Item will have been opened by clicking through from another area of the website, say a News Listing Atom, where it "picks up" the specific News Article ObjectID. This ObjectID will be the focussed objectID.
You can either add an Atom to an individual Web Page or to the Web Page Template - and spread it across all Web Pages built with that Template. The addition / management of Atoms is covered in a separate Help Resource.
Once added onto the page, the atom will start working immediately, with some preconfigured options. This includes the number of comments on the atom (preset is 5).
If you do however want to change these then there are a few options on the atom's config.
This option defines the number of comments that the atom will show at any one time regardless of what filter is being applied to it.
There are two options when it comes to sizing, 'Full Width' and 'Specific'.
As the name suggests, 'Full Width', sets the atom to be the full width of the web page it is on and will change dynamically as the size of the window is changed.
"Specific" on the otherhand allows you to define an exact width in pixels. Choosing this option over 'Full Width' will cause another field to appear, which is the field in which you define the pixel number. This size will remain until the window it is on is decreased to a width below this.
Once you have completed the setup, the web page will display the Facebook comments for the focussed objectID.