(a) I'd call the middle section a carousel, but some people call it a slider.
(b) While I'm not loving that page design, being in the centre, the carousel acts as a focus for the user's attention, and serves to showcase headline content — typically it might feature curated or editor's choice types of content, or "hero objects", things that the site owner/organisation wants to promote at the moment. For instance, if it was a museum website they might want to highlight their latest exhibition and invite people to click through and find out more, but then the carousel might rotate to show something else that's of potential interest too.
When using carousels on a site, it's also worth considering whether you might:
(i) allow users to override any existing transitions and click through the items at their own pace, in case they catch the end of an interesting-looking item and want to go back, or want to browse faster than the site's transitions are set up to do. News sites with tickers showing the latest headlines sometimes do this — The Guardian is one example, though the text is so tiny and the scroll arrows so far away that it's not brilliant from an accessibility point of view:
(ii) include some visual indication that you are currently viewing object X out of a total set of Y. Sites that do this include Epicurious.com - you can see from the little buttons underneath the carousel which object/image is currently 'selected':
Neither of these examples is perfect, or particularly aesthetically pleasing, but I hope they get the idea across.