When you install MuLab / MUX Modular on your computer, it comes with a library full of sounds and effects. This is called the Factory Library.
When playing with the MuSynth, MuDrum, MUX, MuVerb etc and editing these factory presets, you will come up with nice new sounds and effects that you want to save.
When you edit such factory preset and save it using the "Save Preset" button at the top of the editor, the presets will be automatically saved in your User Library, and the factory preset is preserved.
Using "Save Preset As" you can choose any location on your system.
By default your user library folder is located at the User/Library sub-folder in the installation folder.
But you can set a specific folder on your system to be your MuLab User Library folder.
This is done by editing the "User Library Folder" preference.
Similarly you can also overwrite the default factory library location by editing the "Factory Library Folder" preference.
There are two ways to include samples in a MUX preset: Link them or Embed them.
When embedding samples in a MUX preset file, the MUX preset file size will be much bigger as it includes the embedded sample(s).
Embedding can be done via the sample's context menu -> Embed, or via the Project Browser -> Samples -> Options -> Embed All.
When using sample links and you want your project / MUX preset to be used on another system (eg sharing with other users), then it's highly recommended to copy/move the used sample files into an "Audio" sub-folder in the preset file's folder.
Then upon saving the preset MUX will use a file reference relative to the preset file.
So then it's easy to move MUX preset file + sub-folder together (eg. share a preset via a zip file) as thanks to the relative file reference, the reference will stay valid.
Note however that oscillator waveforms are always embedded within the project/MUX preset file, even when you loaded the waveform from an audio file.
Multi-form oscillator 'sample grains' are sample objects though so there the above linking info applies too.