‘Warm glass’ refers to glass slumping, fusing, and other printing processes that occur between the temperature range of 1100F and 1700F. It may not sound warm, but it is compared to the temperature used to blow the glass, which can exceed 2000F.
Another term for this process is kiln-forming. Glass fusing is a process to use the kiln to join pieces of glass together. If heat is applied to the glass, it softens and becomes fluid and flow together.
You may have a look at a guide on fused glass at https://www.artglasssupplies.com/contemporary-fused-glass-by-brad-walker. It will give you all the details on this particular process.
Glass pieces will stick or fuse to each other and when cooled the pieces will be solid and unbroken. Slumping involves the bending and shaping of glass used to make glass kiln heat take the already fused in the form of bowls, plates, or other objects.
Several other techniques are combing the warm glass, which means using a tool to distort the shape of the glass while it is still hot and the fire polishing which involves heating the glass in the kiln just enough to make it smooth and shiny.
The basic requirement is to have a furnace. The ceramic kiln can be used to warm the glass, but if it may be better to use one that has been specifically engineered to shoot a warm glass. It is necessary to monitor the temperature inside the kiln, which is usually performed with a pyrometer.