How do I change the column names and customize. For example A I want Table 1

If you haven't done so already be sure to have a look at the Numbers User Guide at Help > Numbers Help in the menu. The User Guide explains the basics like this. Also check out the built-in templates at File > New.

Column letters and row names are built into Numbers. They are visible when you are working in a table, but not otherwise.

You can enter whatever you want in the Header Rows, Header Columns, and Footer Row to "name" the columns to your liking.

Add or remove rows and columns in Numbers on Mac - Apple Support

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