You will only hear noise from the machine. Yes, you should continue to breathe as you normally do. This is different from having an x-ray taken, when you might be asked to hold your breath. Swallowing also is okay. You will want to prevent that area of your skin from being exposed to the sun, and your physician will advise you of special precautions.
Some treatments do cause skin problems - it's like getting a sunburn.
If you need skin care during your treatment period, advice and treatment including creams will be provided by your physician. This varies from patient to patient. Some can miss a treatment without it causing major repercussions, while for others, making every scheduled session is critical. Patients should speak to their physician about this. Yes, depending on your physician's advice.