Most of the standard library in Julia (which can be found in /share/julia/base and /share/julia/stdlib, relative to where Julia was installed) is written in Julia itself. The rest of Julia's code ecosystem is contained in packages that are simply GitHub repositories. They are most often authored by external contributors, and already provide functionality for such diverse disciplines such as bioinformatics, chemistry, cosmology, finance, linguistics, machine learning, mathematics, statistics, and high-performance computing. A package listing can be found at http://pkg.julialang.org.

Julia's installation contains a built-in package manager, Pkg, for installing additional packages that are written in Julia. Version and dependency management is handled automatically by Pkg.

Pkg has a REPL mode, which can be started from within the Julia REPL by entering the ] key, which is often called the REPL's package mode. The Pkg mode is shown as a blue prompt, like this: (v1.0) pkg>.

From this mode, we can start all functions of Pkg. To return to the normal REPL mode, press Backspace or Ctrl + C.

To initialize your environment, enter the init command, which creates an empty Project.toml file in your Julia installation folder.

Before adding a new package, it is always a good idea to update your package database for the already installed packages with the up command. Then, add a new package by issuing the add PackageName command, and execute it by using PackageName in the code or in the REPL.

For example, to add 2D plotting capabilities, install the Plots package with add Plots in the Package mode by first typing ]. This installs the Plots package and all of its dependencies, building them when needed.

To make a graph of 100 random numbers between 0 and 1, execute the following commands:

using Plots 
plot(rand(100))

The rand(100) function is an array with 100 random numbers. This produces the following output:

After installing a new Julia version, update all the installed packages by running up in the Pkg REPL-mode.