After the vows have been spoken the couple exchange rings. The wedding ring is placed on the third finger of the left hand, also called the "ring" finger. The wedding ring is usually a plain gold ring. I was once told that the third finger was chosen because in the past people believed a vein ran from that finger, straight to the heart - modern anatomy books havel put paid to that theory though.
After the wedding ceremony, the bride, groom, officiant, and two witnesses generally go off to a side room to sign the wedding register. Without this the marriage is not legal and a wedding certificate cannot be issued.
Afterward, guests file out to throw flower petals, confetti, birdseed, or rice (uncooked for obvious reasons) over the newly-married couple for good luck.
The bride stands with her back to all the guests and throws her bouquet over her head to them. Whoever catches the bouquet is the next person to get married. I don't know if this has ever been scientifically tested, but it can result in a very unseemly scramble, reminiscent of rugby scrums.
Finally, a photo session ensues of the couple leaving the church, and everyone has to stand around to form formal groups for the photo album. A lot of people video the whole thing, which can be good for a laugh on YouTube.