To enter data in Excel, first select the cell by clicking on it. Then type your data and press Enter to confirm and move to the next cell. If you want to enter a new line within the same cell (like a line break), you need to press a special keyboard combination:

• On Windows, press Alt + Enter.
• On Mac, press Control + Option + Return (or Control + Command + Return).

This allows you to have multiple lines of text inside one cell. You can also double-click the cell or click in the formula bar to edit the cell content directly before pressing these keys to insert a line break. Additionally, you can change the behavior of the Enter key in Excel's options to control whether it moves down, right, left, or up after pressing Enter, or to stay in the same cell. These instructions work for entering data and creating line breaks inside cells in Excel on both Windows and Mac systems.