Histology is the science of study of thin sections of tissue with a microscope. Once an understanding of normal has been gained the study of abnormal tissue (histopathology) is useful in diagnosis.
Greek. Histos a web
Classical microscopy is by use of light after suitably staining of the tissue.
Less commonly using electrons.
Pictures are often available on the internet. Ganfyd's images are at under Photomicrographs