Tab or down arrown in numbers

Hi there

When I am using text in numbers I press return in order to get down a cell (as I would on any other spreadsheet) and it just adds a new line in the same cell. Is there another key I should be pressing in order to go down a cell when, for instance, putting in my table headers or is the only way to do this to touch the new cell you want? There is a down button and an across button in the number pad but not one in the text?

Thanks

Holly