Download from www.jsoftware.com/files/libsource.zip.
Unzip into any directory, preserving folder names.
To access from PM, you need to define appropriate folder names.
Folder Source should point to the entire directory.
Plot is treated specially - to work with the plot source, also define folders Plot and Plotdev to point to the plot subdirectories.
Examples:
Source d:\jsource Plot d:\jsource\plot\source Plotdev d:\jsource\plot\dev
Each source project is self-contained and can be built by clicking the Build button in PM.
To build all projects, go to project ~Source\build\build and click the Build button.
Note: the source is built into the ~system path and replaces your existing scripts. Back up your system first.