Do It Yourself has an online guide for choosing bifold doors. Lowe's and This Old House also have guides on this type of installation.
The Do It Yourself guide covers topics such as whether to choose wood or metal doors, knobs or handles and picking a good locking mechanism. It also talks about which doors will require maintenance.
The Lowe's and This Old House guides both offer step-by-step instructions. Lowe's offers further instructions on troubleshooting issues such as adjusting the height of the door and making it plumb after installation. This Old House talks through the installation from mounting the hinges to installing the door pulls. Other websites with guides include Home Repair Central, Andersen Windows and The Door Guy.