The lymphnode is where the bad stuff gets filtered to when you have infection, etc in your body. That is why we get swollen glands (which are actually lymphnodes) in our neck when we have a sore throat or tontislitis. Women with breast cancer often have the lymphnodes taken from under the armpits as cancer cells can be filtered to there by the body.
These are the bits that swell if you get the mumps too - there are also ones in the groin. I would say if they stay swollen and sore for any length of time, you should get it checked out by your GP.