A group of similar cells that work together to carry out a specific function its known as a tissue. There are four types of body tissue: Epithelial Tissue, Connective Tissue, Muscle Tissue and Nervous Tissue. We will see one by one with greater detail.
It is made up of cells closely packed and ranged in one or more layers; this tissue covers the whole surface of the body. It is usually separated from the underlying tissue by a thin sheet of connective tissue known as base membrane (This membrane brings structural support and binds the epithelial tissue to other structures).
There are different types of Epithelial Tissue:
Squamous epithelium is made up with squamous cells that look like thin, flat plates. We can identify the type of epithelium with the cell form. These cells usually have horizontal flattened, elliptical nuclei. And they form the lining of cavities such as the mouth, blood vessels, heart and lungs.
Here are some images to help you visualize how the cell looks like.
Source of the First Image
Source of the Second Image
If you would like to know more about this type of tissue, here is a link about it that you should check out.