How Can I Pull This One With WHERE IN

Hello everyone,

For the sake of simplicity let's imagin we have two tables simple tables: Categories(Id, Name) and Products(Id, CategoryId, Name). My question is how can I make a product list, filtered by category, using a Stored Producedure (SP). My objective is to have the SP receiving the list of categories we want to display, as an input parameter, using it in the SQL Statement. Something like:

Procedure:
ListProductsFilteredByCategory
@Categories AS NVarChar

SELECT
   [C.Name] AS CategoryName
  ,[P.Name] AS ProductName
FROM
 Products P
JOIN
 Categories C
 ON C.Id = P.CategoryId
WHERE IN (@Categories);

How could I make this SP work in a way that @Categories can contain an undefined number of category IDs?

Best regards,
DBA