Throughout all 3 Ages in a game, the players will get to build Structures (cards) and Wonders (board).
Most structures have a resource cost. Some are free and some have a coin cost. Some also have a resource cost and a free Construction condition
Some brown cards cost a coin which must be paid to the bank on the turn in which they are constructed.
Some cards have no cost and can be put into play for free.
Some cards have a resource cost. To construct them, the player must produce the corresponding resources AND/OR buy them from one of their neighboring cities.
The Wonders all have a resource cost.