Managing Code - Creating a Library/Package from scratch?

The bit I always struggle with on various Smalltalk environments is the right way to manage code. It keeps changing. Which is fine. But I've been away for a bit and I'm lost now. I want to create a new package that can be loadable and lives in a git repo. I guess Metacello is part of that. And Iceberg. And...what else? I want to build a library but am no longer clear on what a library (or package I guess) definition is built from. Thanks.