Parenchyma cells refer to the bulk/functional parts of an organ. This is in contrast to stromal cells which refer to structural parts of the organ, i.e. the connective tissue.
Below are some examples of parenchayma cells:
Kidney- nephrons
Liver- hepatocytes
Brain- neurons
Ask yourself, "What is the function of this organ?" Then name the cell in the organ that provides said function.
-KG