Slices
Slices are super important in Go. If you're just starting out, the Tour of Go: Slices is a great first stop.
If you want to really understand slices — how they work under the hood and why they behave the way they do — the Go blog has two fantastic posts: Slices Intro and Slices.
For Russian speakers, here's a really good video that explains slices: GoLang Slice в деталях, простым языком.
Source code: runtime/slice.go on go.dev.