A bifold door consists of two panels that are connected with leaf hinges. Because of this fact, they take up half the space when they’re opened, and they’re relatively easy to install.
Top mounting hardware fits into a guide track screwed to the head jamb, and the hardware at the bottom fits into a small pivot bracket screwed to the side of the opening near the floor. The manufacturer’s instructions will tell you how to properly locate this guide track and pivot bracket.
Then it’s simply a matter of installing the guiding roller and the top and bottom pivot studs on the door, using the predrilled holes. The top guide and pivot stud will go in place first, so you can swing the bottom of the door into position and drop the bottom pivot stud into the pivot bracket, completing the installation.