The plunger is slowly depressed and released to, respectively,  expel and draw  the liquid. The plunger may often be rotated to set the amount to deliver, which is seen in a small window in the side of the pipettor. There is usually another "plunger" which is used to remove the tip. Removable tips are placed onto the end of the pipettor by just pressing them on. They are usually replaced after each use.

To use the pipettor depress the plunger to the first stop, immerse a small amount of the tip in then liquid and release the plunger. To dispense the liquid, place the tip against the side of the container and slowly depress the plunger. To get the last bit out of the tip depress the plunger continue pressing the plunger all the way down.

Play1: Shows the basic of the pipettor                            Play2: Shows drawing and expelling of  liquid.
                                     Note how much of the tip is immersed.