Trying to understand sync and backup options

I'm not a technical person, so I'm a bit confused about what are the syncing options. I'd also suggest having such an explanation in your website, if you want the general public to understand their options.

My questions:

1. What is the difference between "third-party sync disks" and "third-party cloud storage services", mentioned in github?:

   Although it does not support third-party sync disks, it supports third-party cloud storage services, which can be configured in Settings - Cloud - Cloud Storage Provider

2. What does this quote mean, from the website?:

   Support Android. Not just a APP, it can also be used as a mobile server, as long as the computer and mobile phone are in a local area network, you can directly use SiYuan on the mobile phone through the computer browser.

What I want:

• For my data to never reach the internet. All my data should stay in/between my devices.
• If possible, I'd also like to be able to use SiYuan on my Android phone, and have it sync with my laptop via local network only (ie. directly, without going through the internet). If I leave the house with my phone, I want all my data to be there - then if I change/add/remove anything while I'm out, as soon as I'm back home I'd like those changes to be reflected in my laptop. I'd probably keep most of my Notebooks exclusively in my laptop, then have one Notebook synced between laptop and mobile.
• I don't want to need to pay for any storage service.

Probably my questions are very basic for you guys, but for someone who isn't technical this is quite hard to understand! Thank you in advance for your help.