What do the symbols on the union jack mean?

ANSWER

Supposing it is the British Union Flag that you are talking about, it's composition represents the Union of Britain, Scotland and Northern Ireland and it consists of the national religious symbols of the 3 territories: St. George's Cross for England, St. Andrew's Cross for Scotland and St. Patrick's Cross for Northern Ireland. These 3 crosses are overlapped one on top of the other to form the Union Jack which represents the British Empire and the Commonwealth since 1801 until the present day.