When you see the default format exposed in the box, you can type over the default text.
Press Tab when you finish entering the columns, then click the top of the box next to the table name. You can resize the table box by dragging any of the points along the edge.
To create a Primary Key or change the Primary Key to another column, you can double-click the table definition in the diagram and use the Edit Table dialog.
The Primary Key is indicated by <<PK>> on a database diagram. You might have to stretch the inside box to show the primary key.
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