Cell Structure

Let's start with the difference between Animals, Plants, and Bacterial cells.
Cells are the smallest form of life that can replicate independently, unlike plant and animal cells that can replicate and duplicate. 
Bacterial cells are a whole organism, they can also fully reproduce asexually, but animal and plant cells are multicellular which are organisms that contain lots of cells. 

If we take a human and put him under a microscope, we will notice that the human is made out of cells, and the skin is made of skin cells, blood is made from blood cells, in our bodies alone we contain hundreds of different types of cells, an adult human can have up to 40 trillion (40,000,000,000,000) cells.

Plant and animal cells are eukaryotic cells.

Let's take a plant and animal cell to compare each other. 
First, they both have a cell membrane that controls what can go in and out of the cell, like a security gate.

Inside the cell membrane is a Nucleus which has all the DNA of the cell both are filled with cytoplasm a type of gel-like substance, and both are littered with lots of Mitochondria which provide energy from sugars like glucose to make energy for the cell, and both have lots of Ribosomes which protein is synthesised.

Plant cells are slightly different from animal cells, one thing that separates the plant cell from the animal cell is the walls are more rigid and made from cellulose, along with a Permanent Vacuole which is a sort of sac which is a mixture of water, sugars and salts, and finally Chloroplast which is where Photosynthesis is done.
For a rough explanation, photosynthesis is when a plant takes energy from the sun and forms sugars like glucose to help feed the plant. 
And plants that do photosynthesis have a green-coloured substance named Chlorophyll, which gives the plant leaves its green colour. 

Bacterial cells are unicellular which means that they are one cell, they are Prokaryotes which are=.