In Excel and in Calc, you can create a carriage return, aka line break, to go to a new line within the same cell.
You do this by pressing Ctrl Enter to go to a new line.
However. In Excel you can do this with your cursor in the input field at the top or in the cell. In Calc, your cursor needs to be in the cell.
Also (thanks to a reader for a note on this). One occasional issue. This applies rarely and only if you've got some serious spreadsheet action. But keep in mind that the carriage return will sometimes be interpreted as a space. Do you care? Probably not if you're not running any evaluations of that cell. But keep this bug in mind.