With a lever filler, opening the lever completely compresses the ink sac, by means of a flat pressure bar operated by the end of the lever.  To fill you simply open the lever fully, immerse the nib in ink and then close the lever.  You need to wait several seconds to allow the ink to be drawn up.  Now lift the pen out, shake any surplus ink off gently and wipe the nib with a tissue.  Done!  It is not necessary to operate the lever more than once.