Factorio 0.17. Belt/inserter tricks - Album on Imgur
Factorio Belt Mechanics, Tipps & Tricks in 5min - YouTube
Factorio 1.0 / 0.18 Tutorial - Inserter, Belt & Splitter Mechanics: New Player Guide - YouTube
Factorio Mod Spotlight - Beltlayer - YouTube
Belt transport system - Factorio Wiki
Detail: The small wall at underground belts is smaller, when a belt is side loading it, visualizing, that one side of the belt can now in the underground. : r/factorio
One picture guide: Basic belt manipulation : r/factorio
Optimal belt balancing in Factorio - Olivier Corradi's blog