To install the Store Locator on Shopify, you must first ensure you have created a page template for your store locator in your theme. You can do this by going to your Themes > Customize. At the top, select Pages > Create Template. Name your template something like Store Locator and you can base it on a different page for now. Click Create Template.
Modify your template as needed for your design purposes. When design of template is complete, click Add Section > Custom Liquid. Here is where you will paste in the embed code which you will copy from the Store Locator wizard.
Next, you want to create the actual Store Locator page, using the template you just created and tie that into the main menu navigation. To do this, first add your page by going to Pages > Add Page. Name your page and set the Theme Template to the Store Locator template you created earlier. Hit save. Now go to Navigation > Main Menu > Add Menu Item. Add the name and then select the page template. Click Add. Click Save Menu. Now when you view your store and refresh, you should see the new menu option which will take you to your installed Store Locator.