Hi @SirJayjay , there will be a coupons option in the left menu:

If it’s not there, you may need to connect your e-commerce platform in Integrations. Here’s a video that goes through coupons in detail: 

@Shaun love the video summary of how to use Coupons and some best practices to get it started. 
@SirJayjay - if you have additional questions about coupons, or how to troubleshoot based on your specific e-commerce platform, you can check out one of the following articles that might fit the bill: 

How to Set Up Coupons for BigCommerce
How to Set Up Coupons for Magento 1
How to Set Up Coupons for Magento 2 
How to Set Up Coupons for Shopify
How to Set Up Coupons for WooCommerce
How to Use Coupon Codes in Klaviyo