You can add a search option to appear on your shopping page via the DESIGN > CUSTOMISE DISPLAY OPTIONS area.
Select your required option using the SEARCH OPTION dropdown.
Default Search By Keywords - Adds a standard search option above your product list
Product Availability by Address - Add a address search field at the top of the list that finds products via Postcode (as set by editing the Product > Stock > Post Code Availability field.
Advanced Search Box Left - Add an advanced search sidebar to the left of the product list.
Advanced Search Box Top - Add an advanced search sidebar to the top of the product list.