Do I need Arduino/Raspberry for every light in my house?

I am a "tech guy" who wishes to learn about home automation (with HomeAssistant.io). There is something I don't understand yet.

I have seen tutorials about how to make my own home own automation Etc. In all of the tutorials I saw a lot of cables crambeling [??what??] to only switch on a simple light (while the Arduino is connected directly to the light and the Arduino connected with an Ethernet cable to the internet and the light turned on by an Android app).

If I want to do a real home automation I don't want to connect every light in my house with a wire to the Arduino (sounds like a crappy home automation).

I understand that there is something called ESP8266, this is a wireless chip.

My questions:

1. How to connect the ESP8266 to a light in my house without direct (wire) connection to Arduino?
2. How to program it?

Assuming that I will connect the Arduino/Raspberry directly with a wire to the router and my home devices will be without any cables going around the house like a caveman.

In your answer please give some good tutorials.

You can control several lights with an Esp2866 or raspberry using wifi and relays outputs, but you have to setup the device on a IOT platform like Blynk Or My Devices Cayenne, both have their own API and documentation you should take a look.