Thanx folks! I think I get it!?
After T/O I use the SID to get to the airway. After that I pass a couple of intersections using radials and distances.
Then I use the STAR to get to my IAF, from which I take up the appropriate approach plate, depending on runway in use and available facilities. Have I understood it?
But then there must be several different SIDs and STARs depending on which airway is appropriate? Things are starting to make sense!
Cheers all and thanks for some very explanetory answers!