Examples include Pelikan, Mont Blanc and other German pens among others.  Unscrewing a knob on the end of the pen pushes a piston down the pen barrel.  Screwing the knob down again pulls the piston up.  To fill, immerse the nib in ink, unscrew the knob fully, then screw it down again fully.  This will fill the barrel.  Now lift the pen out of the ink, shake off surplus ink and clean the nib with a tissue.