Buses in Madrid
The passes valid for the metro system are the same you'll use to take city buses. You can buy a ticket on the bus, at a metro station or at a kiosk or "estanco" (tobacco shop).
Madrid has over 200 bus lines that run all over the city and to the airport. With so many routes, Madrid buses are not quite as easy to navigate as the metro, and less so if you're not familiar with street names. But you should have to problem once you familiarize yourself with the city a bit.
Every bus stop has a city map marking the 200-plus routes that you'd need a magnifying glass to decipher. You're better off referring to the maps that are posted per route, which name the streets that each bus line follows and also indicate the metro stops it passes when applicable.
When your bus stop is coming up, make sure to press one of the yellow buttons, because the driver won't stop if there's nobody else waiting or getting off.