Mostly just collating the excellent responses so far: Creo tables can do things that Excel can't, like setting up instructions for traversing the assembly to make a bill of materials. Excel can do things that Creo tables can't, like being a spreadsheet and referencing the values from cells in formulae to drive other values. To make a .tbl file, make a table in your drawing, and save it as .tbl. The reason for this is to be able to reuse the table in another drawing without needing to recreate it. You can put an Excel spreadsheet in your drawing directly, via OLE. If you want to start with an Excel spreadsheet and end up with a Creo table, you can get the arrangement of cells in the grid and the text in each via .csv.
Right now, that's what you've got to work with. It is a reasonable enhancement request that we look to implementing an import from .xlsx, which would provide column widths, merged cells, note text style, and the like. This would be a significant amount of work, but could benefit a number of customers. Such a proposal would be made a 'product idea', or brought up with the TCs, or the like.
