The SSID (service set identification) is simply the human readable name of the Wi-Fi network which can be visible or hidden (then you have to know it to connect to the network which can make it more secure).
The BSSID (basic service set identification) is the Mac-Address of the router/access-point is a unique identifier of the Wi-Fi network in the following format "00:00:00:00:00:00", which is used from the machine to address it.
BSSID's have to be unique but SSID's don't have to be and there can be more than one.
This is measured in dBm (decibel-milliwatts) and 0dBm corresponds to a Power of 1mW (milliwatt). The scale of dBm is logarithmic and that means that for each 3dBm decrease, the power level is reduced to about one half. A 10dBm decrease will reduce the power level of a factor of 10.
The maximum received power level for Wi-Fi networks is about -10dBm (this is why I default it to this on the upper end).
The channel number is simply an easier way to relate to which frequency your router/access-point currently uses (e.g. CH 1 is the frequency 2.412 GHz).
There are two different bands (frequency ranges) commonly used which have different advantages and disadvantages:
2.4 GHz for better range (especially if walls have to be passed)
5 GHz for better throughput and latency in case there is little in the way (short range and preferable no walls)
The frequencies which can be used depend hugely on your region. This is why I have to know the region in order to give you correct recommendations. The 2.4 GHz band has a maximum frequency range of 2.412 - 2.484 GHz and the 5 GHz band has a frequency range of 4.915 - 5.825 GHz.
A channel is a range of frequencies and no single frequency (this is known as the center frequency).
You should always use a channel which has little interference from other networks because then there is less noise and you will have better throughput and stability. This can be illustrated many different ways. How I do it in my app, I explain in the tutorial "Graphs explained". I also give you a suggestion which channel you should use, you learn more about it in the tutorial "Rating explained".
The protocol is the way a transmitter & receiver communicate, you can say they have to speak the same language to understand each other. Different protocols use for example different modulation-techniques (the actual physical waveform) and different frequency ranges which can impact throughput in an enormous way. The most common ones you probably have yourself is 802.11g or 802.11n.
In order to keep others out of your network, you should also protect your Wi-Fi connection with a secure password.
There are 4 commonly used standards:
WEP (Wired Equivalent Privacy)
WPA (Wi-Fi Protected Access)
WPA2 (Wi-Fi Protected Access II)
Not protecting your Wi-Fi network could be necessary for public hot-spots but in your private home (and of course businesses) you should never do this.
You should also avoid using WEP because it can be broken in a very short amount of time with the right hardware.
WPA2 is the successor of WPA which uses the AES-Encryption instead of the TKIP-Encryption. TKIP was replaced because it reached his designed lifetime and is less secure than AES.
Most recent Wi-Fi access-points and routers default to WPA2. You can check this easily with the help of my app.