Pleade is downloaded using the services of the Pleade collaborative site on Sourceforge. In particular, you can go to the download section to see the list of available distributions.
The last distribution (Pleade 3.59) is available directly by clicking on the icon:
This "executable" distribution of Pleade is available as an archive. Once decompressed, you can launch Pleade directly and use it on your workstation. For more information, see the installation documentation.
To obtain the full sources of Pleade, you must use the SVN services of the collaborative site.