If I understand you correctly, you are looking for resources on how to create an Umbraco Package.
Once you have come up with a way to extend the functionality of Umbraco (ie: a new data type, a new section, some event handlers that are fired on publish, etc), you'll want to find a way to package that up and redistribute it, possibly even on Our Umbraco. There are a couple ways to go about doing this:
The Umbraco backoffice comes with a way to package up document types, data types, templates, assemblies, etc.:
- In the Developer section, expand Packages.
- Right-click Created packages, and choose Create.
- Fill in package details, select content and files, write package actions, etc.
Create packages within Visual Studio using MSBuild. This is a more advanced (and therefore complicated) approach. I've found it helpful to look at the source code of some of the popular packages out there, such as uComponents, to get a good understanding on how this is done.
The package file is simply a zip file that contains xml with instructions for Umbraco on what to do when it is installed.