How do I create an HTML table cell into which I can enter data by clicking on it?

#1
<table>
<tr><td></td></tr>
</table>
#2

You can just add the contenteditable attribute.

<table contenteditable>
<tr><td>Click to edit content</td></tr>
</table>
#3

It is not clear what it is you need to do. If the answer(s) you get do not help then clarify what you need to do.