My name is Aaron, I'm a guru here at Shopify!
No problem at all! What you'll need to do is enter that text into the product template in the code of your theme itself. The file that you'll edit, and where exactly in your code you'll make that change, will vary somewhat depending on what theme you're working with - but it's doable with a little trial and error!
Before making changes to your code, it's a good idea to make a duplicate of your theme and work on that, so that your customers aren't thrown by any unexpected effects on your product pages while you're working. Next, you'll access your theme's code - click on the button with three dots on the theme card, and select edit HTML/CSS. This will take you to a page where you've got access to all the code in your theme - find the one that controls your products, generally named product.liquid. From there, you can try typing in FREE SHIPPING at various points and seeing how it looks on your website!
Hope that's helped! Please feel free to give us a call or start a live chat at any time, we're open 24/7 for your convenience and always happy to assist!
Aaron | Shopify Guru
Hey Aaron, Thanks for your reply but, Can you please add the whole code to achieve that task? and I really think that shopify should have that option to be easy activated from the admin side of the website not by adding any code to the product source page, it can also be done by collections and some of the products can be excluded from the Free shipping, I think this will be a very handy and practical addon.