Pathologists examine tissue at two levels. First, the pathologist examines the tissue with his/her eyes and fingers to find abnormalities. If the piece of tissue is large, the pathologist will cut it into many slices so s/he can find small lesions that may be hidden in the tissue. The pathologist looks and feels for parts of the tissue that are abnormal. She or he looks at the location of the abnormalities and how far a lesion is from the edges of the tissue specimen. The edges are called "margins". For very small tissue samples, all of the tissue is processed to make microscopic slides. For larger tissue samples, the pathologist selects the parts of the tissue that looks and/or feels abnormal as well as some of the normal tissue for processing to make microscopic slides. Most of the time, the pathologist can make a diagnosis based on this first level of tissue examination. However, the pathologist confirms a diagnosis by examining sections under a microscope to make a final or microscopic diagnosis.

http://pathology.uic.edu/understanding-your-pathology-report...

Histopathology (compound of three Greek words: ἱστός histos "tissue", πάθος pathos "suffering", and -λογία -logia "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopathology refers to the examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides. In contrast, cytopathology examines (1) free cells or (2) tissue micro-fragments (as "cell blocks").

The tissue is then prepared for viewing under a microscope using either chemical fixation or frozen section.

If a large sample is provided e.g. from a surgical procedure then a pathologist looks at the tissue sample and selects the part most likely to yield a useful and accurate diagnosis - this part is removed for examination in a process commonly known as grossing or cut up. Larger samples are cut to correctly situate their anatomical structures in the cassette. Certain specimens (especially biopsies) can undergo agar pre-embedding to assure correct tissue orientation in cassette & then in the block & then on the diagnostic microscopy slide.

https://en.wikipedia.org/wiki/Histopathology