A pillar page broadly covers key aspects of a topic relevant to your company (e.g., a product or service), while topic clusters are subcategories that cover keywords related to that topic in-depth.
Google rank all the pages higher if any of the content pages gets hits. The pillar page gathers all the pages which discuss the same topic. In our case the topic could be for example NGS and we could link blog posts, videos, manuals etc. The pillar page would be like table of contents. There is a lot of material about this, like this easy-to-read blog:
How to Build a Topic Cluster
By Sarah Seward | Inbound Marketing Specialist