There are no tutorials for e-commerce website with Gridsome, but if you already know how to build a blog, what’s the problem with building a shop?
You may take a look at tutorial which builds a Food Delivery app.
Create content-type Categories.
Create content-type Product with relation (Categories one-to-many with products).
Create content-type Cart with two relations (Cart one-to-many with products and Cart One-to-One relation with User).
Create content-type Orders with two relations (Orders one-to-many with products and Orders One-to-One relation with User).
Restrict the access to the cart only to the user who created it, by using the owner policy.
Restrict the permissions to Order (Users can only Create orders, but they can’t update/delete, and so on)
Now you can create products, put products inside the cart, create orders, and so on.
You already have 50% of the e-commerce website after all these steps.