An xlsx file consists of a number of components and these posts describe them.
An Excel spreadsheet is normally saved with the extension .xlsx, and other spreadsheet programs will often read and write this format. The basic picture of a spreadsheet is one of rows and columns, the file format offers a more complex set of building blocks that are important to understand.
Here are the general categories that comprise the file structure:
Cells are the building blocks of spreadsheets. Each is labeled with the row (letters) and columns (numbers), so B3 is the second row and the third column. Surprisingly complex things can be stored in cells, and there are quite a few formatting options.
Most things are stored inside cells, but there is also the ability in Excel to have items that float above the cells. Graphs and drawings can be placed here.
The collection of cells and the drawing layer above the cells is collected into a structure called a worksheet. Worksheets are named Sheet1 and so on by default, but can be renamed. There can be a large number of worksheets, so it is possible to create a 3-D set of cells.
The collection of worksheets plus other structures (such as macros) is called a workbook. This corresponds to the file saved on your computer MyExcelFile.xlsx.