Importer products with csv file

Hi

I have a few quistions about importer functionality.

If I want to import some products via the importer functionality, I guess the content of the csv file need to be structured in the same way as the product data are structured in the WooCommerce database.

But how should the csv file actually look like to work.

Is it possible to import products via importer with fx an excel file.

If I export product data from a whole different shopsystem the product data might be a bit different and probably structured in another way. In order to move the product data around so they fit in the import file used to import the data to WooCommerce, it seems to me that this restructuring of data will be made most quickly by using fx an excel file.
If this is possible, how should the excel file look like to work.

Thanks in beforehand