With regards to product classes and attributes, vendors have the following capabilities:
can define product-specific attributes (attribute names) and attribute values for their products;
can create product classes and add attributes for them;
can see product classes created by admin or other vendors;
can see attributes (attribute names) and attribute values created by admin or other vendors at the level of product classes + can assign these attributes and values to their products (but cannot tell whether a specific class or attribute is owned by admin or by another vendor);
cannot create their attributes (attribute names) for product classes created by admin or other vendors;
cannot edit the classes, attributes, or attribute values defined by admin or other vendors;
cannot add attributes (attribute names) at the global level (This feature is accessible only to the administrator);
can see the attributes (attribute names) and attribute values created by admin at the global level + can assign these attributes and values to their products (but cannot edit these attributes or their values).
Depending on how the store administrator configured the Multi-Vendor add-on, vendors may or may not have access to adding values for global attributes and attributes created by the admin or other vendors at the level of product classes. That depends on the "Vendor access to global attributes" setting on the Multi-Vendor settings page. If it is configured to "Use existing and add new values," vendors do not just use the existing attribute values but can also add their new values for the attributes defined by others. If the value is "Use existing values only," vendors cannot add their attribute values and only use the existing values.
Vendors can access the section for the management of product classes and attributes in one of the following ways:
via the Attributes tab of the product details view of a specific product:
via the Classes & Attributes menu item in the Catalog menu:
Check Product Classes, Attributes, and Variants for more information.