The panel produces electricity and save it through the charge-controller which regulates the volume (voltage). The battery supplies 12V to the output devices where we can use a light at 12V through a cigar socket as well as charge cell phones through USB cable. The following picture is a whole set. A couple of solar panels are at the back side and a battery is covered with a box.
In the following photo, the panel's capacity is 6.5W x 2 = 13W.

From now on, I am going to explain the each main devices one by one.

Solar panel

The capacity of the panel is of course dependent upon it of a battery which depends on the electricity consumption. For beginners, 20W is recommended. If the demand is high in future, you can add one or more. In this case, bear in mind the capacity of the charge-controller. I will explain this point latter.
The panels are connected in series.

Charge-controller

This capacity is 10A. This is made in China. This model:Juta CPM12 is so widely sold that I believe this would be OK. This capacity can bear up to 100W panels.
The left green light shows 'charge' that a panel is working and the one next to it shows 'load' that devices are being used. There are two red lights which are on. These indicate the status of the battery. When three are on, it is full. Now its status is a medium level.
The more accurate measurement to read the status of the capacity is to use a digital voltage meter.

At the low part of the machine, there are 6 connections. From the left #1 to #6 are allocated. #1 and #2 are allocated for input from a solar panel. #3 and #4 are for input to a battery and lastly #5/#6 are for output of 12V for useful devices.

It is important that at the beginning of the connection with this controller, you should first connect the battery wires i.e. #3 and #4. Otherwise, the system would be broken.

Battery

This can be obtained everywhere in the world if the quality is not minded. I got freely this used one from my Toyota dealer. I appreciate them because they gave me a good one. A battery generally supplies 12V DC.
In fact, this is the most important device which save and supplies electricity. If this capacity is bigger, we can use more device such as a TV set and other appliances.
The important thing to manage this capacity is to balance input during day time and output during night time.

Devices receiving electricity

From #5,6 of the controller, constant DC, 12V electricity is supplied and then a cigar socket (female) can serve as a universal connection.
The below figure illustrates the usage of devices through a cigar socket..
USB outputs from the cigar socket can widely be sold due to the fact that people want to charge phones in the car. USB is now one of universal connections. In terms of USB. powers, there are 2 standards such as 5V 1A and 5V 2.1A. The latter is powerful because tablets and smart phones require more powerful charge.
Later I will explain more about the devices.