For those of you in the midst of transitioning or preparing to transition to Julia 1.0, I've made a short (less than 6 minutes) tutorial on the basics of the new package manager. This video includes how to interact with the package manager and how to check, install, update, and remove packages.
For more advanced information, check out the documentation and the relevant JuliaCon 2018 talk from Kristoffer Carlson and Stefan Karpinski.