If you want to develop plugins on a larger scale, you can use modern web technologies such as React and webpack for plugin development.
After developing a plugin, in order to install it in Re:Earth, you need to either zip their files beforehand or push their code to your GitHub repository for publication. The former can be zipped by standard function on recent OS. For the latter, you will need to install the git command and create an account on GitHub. We won't go into how to use git and GitHub here, but you can google it and read some useful material right away.
If you want to develop using modern technologies such as React and webpack, you will also need to install Node.js and npm.
Let's go through Tutorial and actually develop a small plugin.