If you’re looking for a thorough primer of Go modules, Bill Kennedy has you covered:

In this post, I will focus on the transition from GOPATH to modules and the problems modules are solving. Along the way, I will provide just enough of the semantics so you can have a better understanding of how modules work at a high level. Maybe more importantly, why they work the way they do.

When you’re done with this, check out part 2 of the series about projects, dependencies, and gopls.