my English is not very good
That is a problem as it is very difficult to understand what you have written. Perhaps you can get some help with your English? Or use a translation web site?
It would also help to know what tables you have defined for this purpose and how they are linked in relationships.
If you have this relationship:
Products::ProductID = ProductDetails::ProductID
and Enable "Allow creation of records via this relationship" for ProductDetails in this relationship.
You can place a portal to ProductDetails on your Products layout and you can enter information about a product in the portal just by entering or selecting data in the fields in a portal row and you can use as many rows in this portal as you need to describe that product.
I got everything but this:
I want a portal to place a dropdown list which in turn selecting something in myself the option, it then a text field in front of the field where I have the lasta of features where you can write the characteristics of my product,
that's what I need to do
But we don't know what it is that you need to do as we cannot understand what you have posted.