Products not showing after import from .cvs

I ve tried to import products from .cvs
The header looks like:
product_code,product_name,categories

The import was done, the categories were set up, i see all the products at administration interface but not in the front end. Allthough the categories are visible also at the front end.

Then I ve deleted the products and reimported the .cvs, but then i got the following message:
"The product is of the type but it already exists in the database and is of the type variant. In order to avoid any problem the product insertion process has been skipped. Please correct its type before trying to reimport it."

Any suggestion?

Thanks in advance

So i ve followed the tutorial, but without success, products are still invisible. I am sure, i am missing something very trivial. I send you the sreenshots, maybe you can find the missing part of the picture...
Thanks

Thanks a lot. Done. The quantity was missing (i m using only catalogue mode).