If you mean what columns should be included in an invoice header table, it depends on the requirements as others have already said. To have ideas how data can be normalized and divided, perhaps the
AdventureWorks[
^] samples would be good learning material.
On the other hand, if you mean how you can find out the columns of an existing table in the database, you can query for example
sys.columns[
^] or use
sp_help[
^]