For those that have sleep apnea. How do you get used to the cpap machine?

Desensitization. I recommend to my patients to try to use the CPAP device in the evening while watching tv to get used to the feeling of the mask and pressure. This helps to make it easier and more comfortable to use at night while sleeping. Sometimes a mask change is needed for comfort or an adjustment in pressure. For some on higher pressure of CPAP and switch to bipap can make breathing easier.
Change equipment. This getting used to is one of the reasons that the american academy of sleep medicine, seven years ago, said for mild-moderate sleep apnea or someone who can't or won't use a cpap, the first line of treatment can be an oral appliance. This should be done by a dentist who has special training in dental sleep medicine.
Other options. If your apnea is severe enough you should feel the diff that shd be an indicator or you may look for cotherapy with an oral appliance.
See answer. I have many pateints with osa, and several of them can not stand the noise of the machine or the constricting feeling of the mask. However, the devices are getting smaller and better and less noisy, and the majority of patients benefit with a good nights sleep and feel much less fatigued throughout the day, making it worthwhile. Be diligent and simply try to get used to it as "the norm.".