The first row of a database or table has to contain the labels for the columns (fields). Microsoft advises you to format these cells as text before you type any of the labels, but there doesn’t seem to be any real need for this action. Generally speaking, a column label that isn’t text is pretty rare, and the General format, which is the default when you type text, seems to work just fine with all the database operations.
Formatting the cells as text after the fact works without a hitch, so there’s even less reason to do it beforehand. The only possible exception would be if you were using some sort of unusual label (like a date) for your fields.
Here’s the database and table creation process, step by step:
Type the field labels in the first row.
Select the range that holds the list of data you entered.
Select Insert Tables Table.
Leave the My Table Has Headers checkbox checked ...