An Excel file consists of worksheets that store data in cells.
When you start Excel, it opens three blank worksheets named Sheet1, Sheet2 and Sheet3 (see the bottom left corner of your file). You can insert more spreadsheets later on (Insert->Worksheet) or delete worksheets if you wish (Right click on Sheet2 and Delete…to delete this worksheet).
Each worksheet is made up of rows and columns. Rows are numbered from 1, 2, 3…through to 65536, whereas columns are labelled with alphabets (A, B, C…through to IV, 256 in total).
Cells formed at the cross-section of rows and columns are identified by their column and row numbers (e.g. the cell at the cross-section of column D and row 5 is named D5). Cell names are very useful in referencing data.