According to the old tradition a groom arrives with his parents at the house of a bride just before a wedding ceremony. In a house of a bride parents and parents in law give blessing to a young couple. Then they go all together to a magistrate (for civil marriage) or to a church (for church wedding). A young couple is driven to the church usually in a rented white car or a taxi or even in a horse carriage. Their car/carriage is adorned with white flowers and dolls.
From practical reasons the preparations for wedding start usually much earlier than just before wedding ceremony. Very often a family from far away arrive earlier, they need to be given a proper welcome, food and also a place to stay. It is not common in Poland to expect the invited guests to stay in the hotels - hotels are just too expensive for an average Pole. So, the houses or apartments of the groom and bride are full of people!
In the past bride was led by her father to the altar and a groom by his mother but this tradition, which is still so popular in the USA, is long forgotten in Poland. So, the young couple goes to the altar together, but it is important to remember that the groom should be on the left side of the bride. They are followed by witnesses, bride parents, groom parents and the rest of the family in the way to the altar.
Both, in church and civil ceremony the young couple is assisted by two witnesses, usually a man and a woman from bride and groom site of the family or a close friend. In Poland it is very unusual to have maids of honor (druzki) and groomsman during a wedding ceremony. I saw it only once on a very rich wedding
Let me add that the wedding ceremony in church must be proceeded by the announcements about the future wedding. Every church has a list of the future wedding announcements which hang on the wall by the entrance of the church. Before being wed a young couple also need to participate in a series of lectures which prepare for wedding.
Roman Catholic Church allows church ceremony wedding of a Catholic and a non-Catholic (even a non-believer) in a church. In that case, a non-Catholic does not participate in the sacrament but the marriage is still considered as valid. The only condition - a non-Catholic partner needs to sign a document that he/she agrees that children will be brought up Catholic.
Since the wedding (especially in towns where people rarely own a single-family house) usually does take place in the restaurant or another rented place - the families cannot afford to invite everybody there. Therefore some people are invited only for wedding ceremony in a church while the closest family and friends are invited for both - a church ceremony and a wedding reception. It is also common that if somebody arrives from a far away place, this person or family is invited for a wedding party.
After the wedding ceremony (Polish "slub", check Polish wedding vocabulary) there is a time for congratulations. After a traditional kiss it is a priest or a justice of a peace who congratulate couple first. While the young couple leaves a church the Wedding March of Mendelssohn or Ave Maria is played by the organist. Then the rest of the invited guests leave a church and wait, usually in a long line to congratulate a young couple in front of the church. The parents and the closest family congratulate first, later the rest of the family. Some quests - usually these who came only for wedding ceremony give only flowers (flowers is a must!) to a young couple.
Except a wedding bouquet, two witnesses usually take care of all the other flowers, it is a heavy burden on them, they are circulating continously between the cars and a church. The flowers are used often to adorn a wedding party. If somebody from invited guests is unable to participate in a wedding ceremony he/she usually sends a telegram or a postcard. If you are invited to a Polish wedding make sure that you check in a flower shop which flowers are used for a wedding rather than the funeral in Poland. Flowers in Poland are very popular and given on many occasions but Poles are very sensitive on which flowers are used on what occasions. Selection of flowers is very rich but the prices depend on the season - flowers are much cheaper in summer and autumn than they are in winter and early spring.
After accepting the wedding wishes from all invited guests but before leaving, somebody usually throws small coins to a young couple (usually on their heads). Then, the money needs to be picked up, mainly by guests. This is an old and pagan habit but still very popular. In the past people showered the young couple with grains, usually millet for a good and prosperous future.
I recommend Polish Weddings Customs & Traditions by Sophie Hodorowicz Knab
An interesting book related to the subject is written by Sophie Hodorowicz Knab, Mary Anne Knab (Illustrator). entitled Polish Customs, Traditions and Folklore