In the perfect world, all devices are connected with a cable, but of course not all devices can use RJ45.
Even though wifi seems simple and easy, getting good and stable wifi is not so simple, I will try to explain why and what you can do to get good and stable wifi.
In general using a cable between 2 devices ensures that you have a stable connection between the 2 devices without interference, wifi signals however travels in air where all kinds of interference can occur from your neighbors wifi, other transmitting devices or even microwave ovens all of these thing can cause unstable wifi.
The right channel
Finding the right channel is important, you need to find the channel with least interference from others, if you live in an urban environment with dense population, chances are a lot of others will be using wifi and most likely on the same channels as you.
To improve your wifi experience you first need to find the best channel for your access point to transmit on, that means examine the airspace where you want to place the access point. You can use different wifi analyzer apps or programs to do so, most of these apps will then show you how many SSIDs are on each channel.
2.4 Ghz was the first frequency used for wifi with 802.11b as the first standard.
2.4 has the advantage of having a longer range than 5 GHz, this however has the disadvantage that your neighbors wifi or other devices using this frequency will interfere with your “airspace”
As 2.4 will use 20 Mhz bandwith but the channels have 5 Mhz space between them, that means there are only 3 channels that are non-overlapping namely 1, 6 and 11.
Here is an example of scan from my home
I have 2 access points with wifi TAN_SLOW one on channel 11 which as you can see is closes to me and then one on channel 1 which is in another part of the house. Then one of my neighbours have an access point operating on channel 4 and due to the bandwith it is interfering with my accesspoint on channel 1 which is why I placed that access point as far away from theirs as possible.