In OpenTTD, Buildings are what make up cities. Buildings are the most common place to pick up and drop off passengers and the only place that accepts goods. The default building set does not contain very tall buildings; this is to ensure that the players can see well behind them. Buldings can be divided into two main categories: Residential and Commercial.
As the game advances through the ages, so to do the buildings, as they evolve from early-20th century brick buildings to modern or post-modern concrete and glass skyscrapers.
Residential buildings range from small houses to a large block of flats. While smaller houses provide smaller amount of passengers and mail, larger blocks will provide more, and they will also accept goods.
There are a few buildings, like churches and football fields, that do not accept or provide mail, only passengers.
Commercial buildings generally accept passengers, mail and goods, and provide large amount of passengers and mail. They only start appearing when the town's population is at least 500, and stations generally need at least 3 of them in their coverage area for it to accept goods.
The Warehouse is an exception - it only accepts goods and doesn't produce anything.