Due to the large spectrum of design alternatives, we rely on the fact your theme has a built-in search element and work with any.
In most Shopify themes there's a built-in search (though sometimes hidden). I suggest you contact your web developer or theme provider to further guide you on including a searchbox. Once it's shown our app will automatically add the instant search magic and search results beauty :-)
If, and only if, you are a brave soul and know your way around the Shopify admin, this will add a generic searchbox in your theme:
1. Open the Shopify Admin ==> Online Store ==> ... Button ==> Edit HTML/CSS (https://help.shopify.com/themes/customization#view-the-customize-theme-page)
2. Locate your main liquid file - usually it's theme.liquid
3. Locate the top header section of your liquid
4. Copy the HTML code to the theme.liquid template:
<form class="search" action="/pages/search-results">
<input type="text" placeholder="Search..." name="q" />
<input type="submit" value="Search" />
</form>
5. Hit Save!