How do you add more data to a table collection view?

I have added a collection. Working in desktop layout, not mobile. When i select “Table” as the collection layout, i only have the option to see one column from the spreadsheet - how do i select which other columns I want to show in the table?!?

Can you explain more about the difference here?

How many columns do you have in total? Can you share a screenshot of the collection setup that does not allow you to view all “columns”, and the list of columns you expect to have?