Plywood subfloor is constructed from thin laminated sheets of soft wood. There are varieties of hardwood plywood available but they are typically used for cabinet making and higher end applications.
Subfloors are designed to provide a rigid flat surface that will allow for the easy installation of the finished flooring product. It is always better to install 3/4 in. subfloor as this provides a more rigid surface.
Plywood subfloors can be cut to size using a standard powered circular saw.