To find out the name of the executable program open a terminal and type in:
rpm -ql lignumcad | less
This will give you a listing of every file installed as part of the lignumcad package. One of those files is the executable program.
Maybe the rpm package name is not lignumcad. Type in:
rpm -qa | less
and you will get the name of every rpm installed on your system.
" are there any special command to start a program?"
Once you find out what the executable program name is for lignumcad then you can type that name in to a command line, create a desktop icon to execute the program, or add it to a KDE or Gnome menu.
Be prepared. Create a LifeBoat CD.