This article explains how tiered link building works by using Tier 1 links to...

https://seo.edu.rs/blog/how-do-i-build-tier-2-content-that-looks-natural-and-not-forced-11162

This article explains how tiered link building works by using Tier 1 links to point directly to your site and Tier 2 links to support those Tier 1 sources