ILETS: Description of a camera

Use the diagram of a camera below to write a description of its component parts and how it works. I was advised to incorporate some sentences. So here is my corrected writing.

A camera is a device which fixes picture of an object on a light-sensitive film.

The case of the camera is divided into two main parts. The first part, which is cylindrical, contains focusing lens and variable aperture that is used for regulation the size of the hole in it. Another part which is rectangular has two cylinders at the sides. One of them is empty, and another has a reel inside. A shutter located in front of this case.The camera is put into operation by a button on it. These two parts are attached to each other and the camera is T-shaped.

By turning the variable aperture, we can adjust the size of the hole which determines the width of a path of light rays from a subject. The size of the hole depends on how bright the lighting is.

The light rays from a subject end up through the focusing lens. Then they go through the hole in variable aperture and a crack which appears when the shutter opens. Finally, the light rays reach the film.

In conclusion, the camera is T-shaped, composed of 2 metal or plastic cases device intended for fixing pictures on the light-sensitive film.

AThe case of thea camera is divided into two main parts

...size of athe hole in...

Byspinningturning the variable aperture, we establish the neededcan adjust the size of the hole which determines athe width of a path of light rays from a subject.

I see that you have used simple sentences. But if I am not mistaken, IELTS looks for a some complex and compound sentences. Therefore, try to incorporate few of those.

This is some great writing!

I found a run on sentence, though:
At the sides it has two cylinders, one of them is empty and another has a reel inside. --- Can you see how this is a run on sentence? It seems like it is not a run on sentence, because the 2 parts contribute to the same idea, but actually you need a period or semi-colon.

At the sides it has two cylinders. One of them is empty, and another has a reel inside.
or
At the sides it has two cylinders; one of them is empty, and another has a reel inside.

I think you should add one more sentence to the end... a sentence that is about what the device looks like rather than what it does. You did a brilliant job of describing what it looks like, but you should probably end it with a sentence about what it looks like instead of what it does.