A spreadsheet is made up of lots of little boxes called *cells*. Each cell can hold a number, some text, or a formula which performs some arithmetic on numbers.
Each cell refers to a specific spot in memory.
Each cell also has a unique address; cells are addressed by a column-letter and a row-number. If you're familiar with the old game "Battleship", you'll be quite comfortable with cell addressing.
| A | B | C | D | |
| 1 | A1 | B1 | C1 | D1 |
| 2 | A2 | B2 | C2 | D2 |
| 3 | A3 | B3 | C3 | D3 |
| 4 | A4 | B4 | C4 | D4 |
Each cell has a particular data type, depending on what's in it. Although it looks as if there are a ton of different data types, there are really only three.
You can format numbers to appear as currency ($), percentages (dates and times. All these and more are represented inside the computer as a number. Dates can be especially tricky, because at first glance they look like they're text.