What should I do if I experience a seminal emission (janābah) and cannot perform ghusl due to the unavailability of warm water, and I only have enough water for wudu'? Should I perform tayammum? And what is the method for tayammum?

If you can heat the water and bathe with it without harm, then you must do so. If you cannot, then you may perform tayammum (definition). The description of tayammum is: you make the intention and say Bismillah, then you strike your hands on the dust and wipe your face and your palms up to the wrists with them. If you strike twice, once for the face and once for the hands, it is more cautious.