While the main Jsoftware repositories were formerly stored in SVN, current repositories and J internal sources are stored in git, hosted on github. However, git can be used to read SVN repositories.
Linux users should have no trouble installing and using git--it was created by Linus Torvalds, the creator of Linux.
Windows users may find this more difficult, so may want to use one of the git GUIs, such as Git Extensions.
If you are interested in understanding the structure of git repositories and git commands, Mark Lodato has put together a solid overview.
(Note that in many contexts, including generating github pull requests, use of git also requires use of Secure Shell ssh.)
See also: https://git-scm.com/download/ which summarizes some popular ways of installing git on Linux, OSX, and Windows.
Typically, once you have reached the stage where you can test the code you are interested in, working from the command line looks like this:
- git pull this brings your local copy up-to-date with the remote copy
- edit your copy to make changes
- git add filenames(s) this tells git what you consider to be important
- git commit This creates a new local version with those changes
- git push This updates github with your new version
Often, the git status command is recommended -- this will list uncommitted changes. In this context the .gitignore file can be useful to hide irrelevant machine created files.
Any of these commands, may require a certain amount of configuration. git commit command in particular expects you to have configured git with your text editor.