There are several different types of collapsible dog crates and almost as many folding mechanisms. However, the most common collapsible crate is the metal cage. It is the most versatile, therefore the most purchased of all dog crates. No matter the size or the manufacturer, the folding process is fairly similar for all of them. You won't need any tools because most of them snap together with existing clasps. You will need to read the manufacturer's instructions to see if the folding process is panel specific. Some have a particular order in which to fold the sides.
How to Fold a Collapsible Dog Cage
Folding a Collapsible Dog Crate
Make sure the door or doors are securely closed.
If necessary, remove the plastic pan in the bottom of the crate.
Detach the end/door panel from the top panel hooks and push toward the interior of the crate until it is flush with the side panel. Repeat the process on the opposite end panel.
Grasp the top panel and lower it to the side until the crate is completely flat.
Secure the crate in the flat position with the hooks provided.