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, to avoid conflicts with KDE 3.x ports. 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.