This article breaks down tiered link building by explaining how Tier 1 links go...
https://touch-wiki.win/index.php/How_Do_I_Explain_Tiered_Link_Building_to_a_Client_Without_Jargon%3F
This article breaks down tiered link building by explaining how Tier 1 links go directly to your site, while Tier 2 links support those Tier 1 pages