If your application depends on KDE 4.x, set USE_KDE4 to the list of required components. _build and _run suffixes can be used to force components dependency type (e.g., baseapps_run). If no suffix is set, a default dependency type will be used. If you want to force both types, add the component twice with both suffixes (e.g., automoc4_build automoc4_run). The most commonly used components are listed below (up-to-date components are documented at the top of /usr/ports/Mk/bsd.kde4.mk):

KDE 4.x ports are installed into KDE4_PREFIX, which is /usr/local/kde4 currently. This is achieved by specifying the kdeprefix component, which overrides the default PREFIX. The ports however respect any PREFIX set via MAKEFLAGS environment variable and/or make arguments.