It is not standard possible to put a store locator in your webshop. Navigate via the left menu of the back office to App > App store. Here you will find an app called StoreMapper store locator especially for adding a store locator. Pay attention! This app is not free.
Prefer to add your own Store locator? Then you have to paste the code of the Store locator into the HTML code of a text editor or into the template editor. Pay attention! Only do this if you have sufficient knowledge of HTML and CSS.