First, get yourself introduced to the language syntax and mechanisms by doing the tutorial you can find on the language website here. It is very concise, and it'll give you a very good overview of what you can achieve with Golang.
Once you are okay with that, you can jump right in and start experimenting. Of course, you can also still checkout more docs and tutorials if you're the study type ! (Checkout github.com/golang/go/wiki/Learn, you should find something).
Since I suppose you're gonna want to code an API, I would definitely recommend to begin by looking at 2 things. They are at the core of any web-service API.
You can check Gin-Gonic, which is the most popular, but you can also check Iris, Mux or any other you find attracting !
The choice is large here, I personally use Gorm (it has bindings for most popular SQL databases), but you can also checkout mGo if you use mongoDB for example.
Happy coding !