The Harvest... menuitem, which is located in the File-Menu, opens a dialog where you can point TMNav to the harvest model file.

Just browse to the appropriate model file and click ok. TMNav will start the harvesting process and present you with the results as soon as the process is finished.

The Harvest...-Dialog is very akin to the Open Map-Dialog, as well as the handling of a harvested topicmap is similiar to the handling of any other open map. Please read the chapter about opening topicmaps in order to get familiar with the more general aspects of the dialogs and of the handling of topicmaps in TMNav.

See the document about TMHarvest for more information and further links.