Modules source path is path that points to a directory that contains Tangra modules. Usually after installation of TF your modules are located in tangra2/tcc/scratch/modules/.
From the main menu choose Settings → Modules source paths. A grid will open. Click on “Add new modules source path” and fill the form field with the full path to your tangra_modules dir.
Note: Please note that modules in this directory will be updated by TCC (when you request that) so your web server must have write privileges to it.