In my copy of Numbers, Wrap text is the default setting.
If yours is set by default to not wrap text, you can easily change that setting for one or more cells.
Select the cell(s),
Click the format brush to open the Format Inspector
Choose the Text section.
Check the checkbox indicated by the arrow to Check (to wrap) or Uncheck (to not wrap) text in the selected cells.
Full view of the table shown above:
Text in cells C3, B4 and A5 was entered directly from the keyboard.
Text in C3 was copied, then pasted into cell B5.
Body cells in rows 4 and 5 were set to NOT wrap text in the cell, letting it flow into the empty cells to its right.
Cell C3 was set to Wrap text in the cell, making the cell (and the rest of the row) expand vertically to accept the extra text.
Regards,
Barry