Press Alt + Enter in Windows
Press Control + Option + Return on Mac
Turn on Wrap Text if you want the cell to display multiple lines
In a formula, use CHAR(10) for a line break in Windows
In a formula, use CHAR(13) or CHAR(10) depending on your Mac setup
Double-click the cell or press F2 before using the shortcut to edit the cell
Use the formula bar and insert the line break where needed