To install .ssp scenery files you need the Scenery Manager, available here: http://www.sailsimulator.com/archive/ss ... anager.exe
After you have installed the Scenery Manager, start it and select 'Install' and then 'Install from a single file', press the browse button behind it and select your ssp scenery file. Then press 'Next' and select where you want to install the scenery. We normally choose the 'Default scenery folder'. Then press 'Install' and the scenery will be installed. Afterwards you can find the scenery in Sail Simulator in the menu 'Environment'->'Sailing area'. In Motorboat Simulator it is 'Environment'->'Scenery'.