Assuming you have a standard auto-siphon...put the racking cane with the 'stick' connected to the hose inserted in. Submerge the tip, and slowly pull the stick up. You'll see some beer climb inside the larger tube...Before you pull the inner stick out, slowly plunge it down and you'll probably see beer coming up through and out of the tube. Sometimes it may take a pump or two to get good suction.
Remember to try to keep the end of the hose submerged in the bucket or keg, and keep it from splashing, to minimize effects of oxidation.
I know those aren't the correct terms for the auto-siphon parts...but I'm trying to keep it simplistic.