Hey @romeoxu 

Welcome to the community and congrats on your first post!
 
From what I can understand, it sounds like you'd like to build out a Flow that will send out emails to your customers when new products are added to your store. 
 
Unfortunately at this time Klaviyo does not have an automated way to send out a flow when there is a new product available. I can absolutely put this in as a feature request for you if you'd like!
With that said, you could send out Campaigns to notify your customers of the newly released products.
 
You can also feature your products in emails using Product Blocks. You can populate these products from a feed or you can manually select which items you'd like to feature in this case. 
Here is a guide with step-by-step instructions for how to use product blocks in your emails: How to Insert a Product Block 

Hope this helps!