Eunice here from Shopify, thanks for posting, and welcome to the Community!
From your message, it sounds like you're looking to create a separate page solely for newsletter sign-ups, is that right? Newsletter sign-ups are usually located as a section on the homepage. Is there a reason you'd like to have this on a separate page instead? My concern is that customers won't have much incentive to visit this page, therefore reducing your chance of building a subscriber list and sharing the coupon code.
Here's a couple of ways you can achieve your goal without having a separate page:
1. All free Shopify themes have a newsletter signup section that you can add to your homepage. If your theme doesn't include a newsletter signup form, then you use an email marketing app, such as Seguno to add one. With this app, you'll also be able to create an email containing the coupon code which will be automatically sent to the customer once they've subscribed.
2. Install a third-party app such as Poptin. This app allows you to create a pop-up that will display when a customer enters or exits your website. On the pop-up, you can invite them to subscribe to your newsletter, as well as display the coupon code for the other website.
I hope this helps. If you have any questions please feel free to respond here.
Thanks for your reply,
I need a separate page as i want to drive some of my Etsy customers on my website (with a link to the page) giving them the chance to get 15% off after subscribing.
I kinda managed to do something that gets close to what i want, have a look at https://obprintshop.com/pages/newsletter . Let me know if you have any suggestions for improving it.