So I just started watching Eli The Computer Guy's videos on networking and I really like them so far(only on the introduction so far though), but I was a bit confused about some of the stuff and I thought to myself that some of this might be obsolote or not so much in use these days/different. So here are some questions(now bear with me, I'm still a noob to the whole topic of networking):

-Are Eli's videos on networking obsolete(besides the speeds that he talks about), what you recommend some other tutorial, if so which one?

-Is a switch necessary for a small network?

-Do we still connect routers to modems or do we just use what we refer to as a router(a mix between a router and a modem -> gateway/gateway router)?

-Can you connect an ethernet cable to your router/gateway?

-So according to Eli if you have multiple routers they make seperate networks that cant just be acessed from each other, then how come it be that I can access my rasperry pi when I'm connected on the network of one router when the raspberry pi is connected to the network of another router and how come it be that once you have the wifi password you can connect to all of them?

I know very little about networking.
So I've got this modem and I am trying to configure it, I am supposed to access to it through a web browser using its IP address. I pinged the broadcast to find the IP, but when I am trying to connect I have a nice "connection refused". So any ideas ?