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In Inspector,Text, Bullets, turn Text Bullet on, as you've already done.
When you begin typing the first entry, the first bullet in the cell should appear.
When the first bullet entry is complete, use Option+Return to take you to the next (empty) bullet point down within the cell...
The cell should expand downward to accept each new entry. (I typed in the lowercase letters following each bullet for the illustration below)

To make it easier to edit the bullet points in the cell, drag the double-line (looks like an equal sign) slider that appears in the far right lower corner of the 'EDIT' box, so the edit box becomes large enough to display all the cell contents.

Incidently, Option+Return also works to make multi-line cell entries without bullets too. I often use it for long descriptive text in column or row border cells.
Message was edited by: kostby