Hi Raphael
You can imagine the architecture of a network at home like this:
There is a home highway with a speed limit (intranet or home network). This highway runs through the switch and has a speed limit of 100 or 1000 Mbps, depending on the switch. This speed is shared by all those currently on the home highway (e.g. your PC, your friend's PC, the TV and the mobile phone connected via the WLAN). Then there is an exit from the home highway into the public transport network (Internet). This exit is formed by the modem and the speed at which you travel there is determined by your contract with the internet provider (you write that you travel slowly).
When you buy a NAS, you connect it to your home highway. Data (at home) is uploaded from the PC to the NAS at the speed specified by SWITCH. At the same time, you can access the Internet at your normal speed.
The situation is different if you access the NAS at home via the Internet (e.g. from work). Then the data goes via modem and shares the speed with everyone who is also surfing via your modem. However, internet access always remains possible in this constellation, it just becomes slower.
-The explanation contains technical inaccuracies to make the text easier to understand.
Best regards
Juy

Connect... The big problem is that I have a very very slow internet connection and therefore I don't want to connect the NAS to the modem!

So if I have understood this correctly, I could load the data from my PC via the switch to my NAS without the data having to flow via the modem/router?

I assume that during such a data transfer I can't access the internet or that both simply take much longer...

Would this version have any other disadvantages?
Which ones?

Can I have the same internet speed during normal use as without a connection via the switch?
For example, when the NAS is off?
Or vice versa, when the PC is not running and I want to access the data... Online?

Many thanks in advance

Raphael