As NuneatonMan says, Gail, it's all quite simple
Whilst the pump blows air into your airways, it is not making you breathe. It is simply pressurising your air passages, a kind of air splint, if you will. It does seem a bit unnatural, but it really is very easy to get used to. It is impossible for the CPAP device to force air into your lungs. Your body simply won't let it, so you can breathe out quite normally when using it, although you are breathing out against a modicum of pressure, which is what most people take a while getting used to. I now uses a BiPAP device, which lowers the pressure on the outward breath and increases it on the intake. Much more pleasant
Each mask has a vent of sorts for exhalation purposes. This is also so that the CO2 that you exhale is vented out of the mask.
Some people take to it easier than others. I found it very easy but I have seen people take weeks. But don't worry. Your clinic will help you get the right gear and make sure you are complying with the therapy
Karenboj, thank you for your kind words. It was my very intention to simplify and clarify the process and hopefully show potential CPAP users that it's not a horrible thing and show non CPAP users what it's all about and why it is SOOOO very important.
It also helps that I'm a Trainer by profession
Anyway, good luck with your CPAP