We will explain in the following order:
1. Programming languages that cannot install libraries
The following programming languages cannot install 3rd party libraries (for now):
C
C#
C++
2. How to install libraries generally
Note ☝️
You cannot add libraries from running a command!
(For example, running npm install will not work for JavaScript.)
So in this article, we will explain how to add them manually.
Click the hamburger menu button.

Open the file that manages libraries from the folder list.

Note ☝️
In this example we are using JavaScript, so the file in question is package.json.
For other languages, the file names are listed below:
Java - pom.xml
PHP - composer.json
Python - requirements.txt
Python3 - requirements.txt
Scala - build.sbt
Perl - cpanfile
Ruby - Gemfile
Swift - Package.swift
Kotlin - build.gradle
Go - go.mod
Add the library you would like to use.

Note ☝️
In this example, we will add the popular library lodash.
Note ☝️
Please look up how to manually specify libraries (it is different in every programming language)
Click "Run" to install the library.

You can see the result on the console.

Note☝️
Any errors would appear here if something went wrong.
That's it! Good luck :)