The answer depends on the specific location and time period, since wedding traditions changed during the very long medieval era.
In early 12th century England (to take a specific example), Church law stated that two people were married when they both agreed to take each other as husband and wife - no ceremony, no priest, no vows and no witnesses were required. This naturally led to many legal difficulties in court cases when one or other partner denied that the marriage had taken place, with much wrangling about who got what part of their joint property.
As a result, by the middle of the 12th century, the Church was encouraging everyone to be married by a priest in front of witnesses and although this was still only a voluntary arrangement most people chose to celebrate with a ceremony.
The bride and groom went in procession to the church, with family and friends, musicians, flowers and singing. The ceremony took place at the church door - outside, not within the church building. The priest conducted the service in Latin, including the vows, with the bride and groom answering "volo" (I wish it), a blessing by the priest and a ring being placed on the bride's finger. Afterwards the party entered the church to celebrate a Latin mass at the altar, with the altar cloth being draped over the kneeling bride and groom.
A silver penny was given to the priest as a donation - in reality this was payment for the service.
Then a joyful procession with music, dancing and singing back to the couple's new home. The priest would later bless the marriage bed - with the bride and groom already in it.
Marriage was not permitted during Advent or Lent. It was a serious offence to marry off a daughter without the permission of the feudal overlord (in some cases this would be the king himself); consent of parents or family members was not required. Marriage was forbidden to anyone who was already a member of the Church, or to people related to each other, or to those already married, or anyone charged with any offence in law.
Church rulings of the 1150s and 1160s stated that "there can be no espousal or marriage before the age of 7". In the 1170s, 12 was made the critical age.
Banns were first introduced into England in 1200 and made law in 1215 (by the Fourth Lateran Council).