EncryptKeeper’s explanation is perfectly concise and informative if you have a cursory grasp of self hosting and networking.
If it’s not making sense to you, I would suggest revisiting some of the technical fundamentals of self-hosting, which admittedly is quite an advanced topic that most people don’t, and do not need to care about.
You would be equally well-served, perhaps more so (if you don’t really care about privacy or terms of service) by sticking to regular cloud services. The road to self-hosting is arduous and if done wrongly, causes you more harm than good. Especially if your technical foundation is not yet strong. Which your posts suggest is the case.