The new code infrastructure introduced in Praxis LIVE v2 allows components to be defined and re-defined at runtime. However, you do not need to code to benefit from this new functionality. There is a growing repository of custom components that you can import into your projects.
https://github.com/praxis-live/pxg
Custom components are defined in .pxg files. To import a custom component into your project, simply drag the file from the File Browser tab into your graph editor. Custom components are only currently supported in the graph editor.
If you find yourself using a custom component regularly, you can also add the .pxg file to the Palette. Use the pop-up menu on a palette category and select Import .... Make sure to use a suitable category, remembering that some categories will be filtered out depending on the type of graph you are editing.
Unlike built-in components, the code that defines custom components will be stored in your project itself. This keeps projects self-contained - you do not have to copy the custom component files alongside your project.
You may notice that the text of a .pxg file is very similar to that of a .pxr file - in fact, a .pxg file is effectively a sub-graph. These files are not just for custom components, and you are not limited to a single component in the file. They may be used to export whole configurations of components for re-use.
There is not currently an export function in the graph editor. However, it is very easy to create a .pxg file. Simply select the component(s) you want to include and copy & paste them into a text editor of your choice (eg. CTRL-c in the graph, then CTRL-v in your text editor). Make sure to save the file with a .pxg extension.