Code playgrounds are places where you can practice- test out your code and see it in action. Some of these playgrounds are used by developers and facilitate collaborative work on projects. Others are more geared toward teaching programming and offer or accompany tutorials and supplemental instructional information.
If you're interested in computer programming, you'll need a good text editor. Many of the best are available free to use and are open source.
To upload your files to a server, you need a tool- FTP (File Transfer Protocol) clients are the standard way this is done. Some servers offer other options (such as setting up remote network connections) but almost all will allow you to use FTP.
All Web developers use tools to help them - even if they code everything manually. Having an error console is a must for developing with JS. Using element inspection tools can make even the most complex websites easy to decipher and update. All of the major browsers have built-in developer tools that are, for the most part, identical. Other tools are stand-alone or can be added as browser extensions.