Nitrogen makes up almost 80% of the atmosphere by volume. Gas can be cooled down and pressurized to make liquid nitrogen. Liquid nitrogen is cold, inert, colorless, odorless, non-corrosive, nonflammable liquefied gas with a temperature of - 196 °C/ - 321 °F. It immediately boils in contact with a warmer object, so basically any object on room temperature. As it causes frostbite on any tissue use of cryogenic gloves as well as goggles is recommended.
Look inside the Dewar flask and notice the bubbling liquid. Liquid nitrogen boils at room temperature. Condensed water vapor forms the fog above the liquid nitrogen. However instead of rising like steam, it sinks.
Two objects of different temperatures, when put in contact with one another exchange thermal energy. This causes the warmer object to cool and the cooler object to warm. Cooling a solid only lowers the temperature of the solid, but the solid will not change states. Some materials get harder while others just get brittle.
If you immerse flower in liquid nitrogen it becomes very cold, water molecules rapidly crystallize to form ice so the flower becomes more rigid and fragile. So on one hand you could "prepare" easily breakable flower, marshmallow or a gumdrop, and on the other hand you could hammer a nail with a banana. Dependable on the size and mass of the object used it will prove to be hard or easily breakable after being frozen in liquid nitrogen.