I don't know anything about CPAP machines. But I suspect there are a number of different types. If so, it might be worth investigating finding one that runs off 12V AND is efficient and therefore uses less power.
Solar panels and batteries are expensive AND heavy. So any research into this may be worthwhile.
In any case, the starting point for any off grid installation is to determine your daily power usage. If you are intending to get a three-way fridge and run it of gas when off-grid, then your CPAP machine may be a significant part of your power usage.
Terminology in any field is always daunting at the start. But after a while the mist clears and it becomes clearer. The more you understand the more chance you will have of going away and not having many problems and being able to fix or workaround many of those that do occur. That will make camping trips less frustrating and more enjoyable.
In my opinion, you will need is a multimeter if you haven't already got one. Reasonable ones can be bought at Altronics or Jaycar for around $20. Get one that can measure at least 10A DC. If you want to splash out, a DC clamp meter is a better alternative and can be bought on eBay for around $50.
If you have any further questions or help in understanding the terminology, don't hesitate to ask. There are a few people on this forum who have gained a lot of knowledge in this subject both practical and theoretical.
cheers
Mike