But where can I find what numbers are mine SPI pins?
On the home page, there is a Products link. On that page, there is a picture of each board that is a link. On each of those links, there is a section that talks about SPI pins. For the Mega, it says:
SPI: 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS). These pins support SPI communication using the SPI library. The SPI pins are also broken out on the ICSP header, which is physically compatible with the Uno, Duemilanove and Diecimila.