The basic rectangular building blocks of a spreadsheet are cells. These cells are arranged in rows and columns to form a grid. Each cell can contain data, such as numbers, text, formulas, or functions. Cells are identified by their unique row and column coordinates, such as "A1" for the cell in the first row and first column. Spreadsheets are used to organize, calculate, and analyze data, and cells are where you input and manipulate that data.