Start learning Julia

What to do first

Download and install Julia via https://julialang.org/downloads/
Read the "Getting started" section of the Julia manual https://docs.julialang.org/en/v1/manual/getting-started/
Do the introductory tutorials in https://github.com/JuliaComputing/JuliaBoxTutorials
Take a look to the official Julia learning resources webpage https://julialang.org/learning/
Open an account in http://discourse.julialang.org/. This is a great place to ask questions and interact with the Julia community.

Setup your favorite text editor or IDE to work with Julia code (see VIM as Julia IDE, or Juno as Julia IDE, or Visual Studio Code as Julia IDE)
Choose your favorite development workflow and read the corresponding guidelines (REPL based workflow, Juno based workflow). For more information read the workflow tips in the official Julia learning resources.
Read the documentation of Pkg, the Julia package manager (sections 2., 3., and 4. are the important ones) https://julialang.github.io/Pkg.jl/v1/
Create your first Julia package (see How to create a new Julia package)
Implement something in your first Julia package as an exercise.
Make sure that you have followed the performance tips in your test project https://docs.julialang.org/en/v1/manual/performance-tips/index.html
Make sure that you understand multiple dispatch and the Julia type system. (See sections https://docs.julialang.org/en/v1/manual/types/ and https://docs.julialang.org/en/v1/manual/methods/ of the Julia manual)

Read the Julia manual https://docs.julialang.org/en/v1/manual/
Ask to Gridap developers.
Open a question in http://discourse.julialang.org
If you are certain that you have found a bug in Julia, report it via the Julia issue tracker https://github.com/JuliaLang/julia/issues