First of all, I would like the text in a cell to change lines (start a new line automatically). To do so, I click on:
Format -> Cells... -> Alignment
-> Wrap text automatically -> OK
Then, I start typing. I press Enter.
Here, the row height is automatically adjusted.
If I decrease the row height by dragging the line between row header 1 and row header 2 on the left, the cell will look like this:
row header 1 and row header 2 on the left:
I have just increased the row height.
Alternatively, I can select the cell and click on:
Format -> Row -> Optimal Height... -> OK