I have to add layer navigation in vendor categories( multi-seller)
Each seller has own products and category.
The Main store has a different category.
The main site category page all are working fine
same functions have to implement in custom category module.
List pages have to filter based on product attribute value.
Go to Catalog > Attributes > Manage Attributes, select yout attribute, there is a dropdown "Use in layered navigation", select "Filterable (with results)"
Also make sure that your category has "Is Anchor" enabled and the attribute you want to use for a filter is either dropdown, price or multiselect.