Browse templates define the display of a single product in the product listing. So you can only modify the contents of the boxes, which are filled with product information in the product listing of a category. The number of those "boxes" - which are displayed in a single row of the product listing - can be changed in the Category Form of that category (see Number of Products per row) or globally in the Shop Configuration (for the case that no category_id is passed to the Shop).

Browse (or product listing) templates can be found in /themes/VM_THEME/templates/browse/.

They are loaded and filled with content in the file /administrator/components/com_virtuemart/html/shop.browse.php.