Elaboration of PBN is Private Blog network. Which means, building a network which is private and where you have the full control. Usually a private blog network builds for a niche site. Though big marketers and business blogs have said that content is king, but till now backlink has an important effect on the ranking of a site. If you want to build manual link to your site from authority sites, then it is very tough. On the other hand, if you build links from your own domains, then it is easy to you and you can expect a good ranking in the search engines.
The first thing of PBN is buying expired domain. And every domain should be hosted in different hosting. After setting up the domain, the next step is building quality content for those sites and linking to your money site or niche site. Though it sounds easy, but the task is complicated. Only the Pro marketers can build a PBN without keeping any footprint.