The Ring, an unending circle, is a symbol of eternity.

The Wedding Ring is the outward expression of an inward bond, as two hearts unite as one, promising to love each other with fidelity for all eternity. 

The circle of a ring represents undying eternal love and devotion and the continually renewed vows of the married couple. In traditional religious ceremonies the wedding rings are being blessed, imbuing the rings with protective powers. 

Commonly the wedding ring is worn on the left hand. the Romans believed that a vein ran directly from the left ring finger to the heart. Left or right ring finger is a matter of tradition and etiquette of the country you are coming from. 

Traditionally the best man is keeping the rings during the ceremony before the ring exchange. Sometimes a ring bearer, usually a young boy connected to bride or groom will carry the rings on a special pillow. You need to explain what a ring bearer has to do because some boys think they are ring bears and growl at you. 

Why do we wear the Wedding Ring on the forth finger?

I found a beautiful and convincing explanation in the Chinese Culture.

The Thumbs represent your parents. Second fingers, the index fingers represent your siblings and the middle fingers are Your-Self. The forth fingers represent your Life Partner and the little fingers represent your children.

Open your palms and let them face each other. Bend the middle fingers and hold them together - back to back. Now open and hold the remaining three fingers and the thumb of both hands - tip to tip.

Now, try to separate only your thumbs in this position. Your thumbs representing your parents,  will open, because your parents are not destined to live with you lifelong and have to leave you sooner or later. 

Join your thumbs as before and separate your index fingers, representing your siblings. They will also open, because your brothers and sisters will  have to live their own separate lives.

Put your index fingers back together again and separate your little fingers, representing your children. They too will open, because your children will move out one day and need to settle down on their own.

Finally, join your little fingers again and try to separate your ring fingers, representing your spouse. You will be surprised to realize that you CANNOT...because Husband & Wife want to remain together all their lives - through thick and thin!