Download the Sony A900 Manual
The Sony A900 Instruction Manual is a 174-page PDF user guide that is available for download as an Adobe Acrobat PDF document.

The owner's operation guide is available for four regions, United States, Canada, Brazil and Latin American. Right-click this link to download the US version directly to your hard drive.
If the above link doesn't work, or if you want another version of the manual, go to Sony's eSupport Center for DSLR cameras, and manually make the necessary selections to download the DSLR-A900 manual.

Unlike Nikon product manuals, Sony doesn't restrict the printing of this document to only those with a serial number.
The printable document weighs in at 3.5 MB (megabytes).
The guide discusses the features of the A900 and how to use the camera, for instance, how to use the supplied IR (infrared) wireless remote commader, the Sony Alpha RMT-DSLR1, on page 30 (the screen capture below is of page 31):

For those who prefer an RF (radio frequency) wireless shutter release remote, consider the Phottix Cleon S6 or Mega Cleon S6 (same functions, but features a more powerful transmitter). Read my reviews of the Nikon and Canon versions of the Cleon to get an idea on how the remote operates.
The receiver unit of the Cleon plugs into the remote terminal on the left side of the A900, as shown on page 40 of the manual:
