What are cells???
and also there example

Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. ... Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Example are plants and animals. The cells of a multicellular organism may share common features and functions. These cells that act as a unit make up a tissue. The fundamental types of tissues in animals are epithelial tissues (or epithelium), nerve tissue, connective tissue, muscle tissue, and vascular tissue.

Afine-grained igneous rock forms as a result of slow cooling.