I'm pretty new, but I've found a few ways. Most useful to modern development is a package called Iceberg, which is a git interface...you can export your classes

I'm pretty new, but I've found a few ways. Most useful to modern development is a package called Iceberg, which is a git interface...you can export your classes/code/etc, commit them, and pull them into different images. You get to choose what you export, so you can only export your code. There's also Monticello which is similar, but uses different repository types than git. You can also just "File out" a class or package, which exports it to the file system.