Sure, here's a basic database schema for an online merch store:

**Tables:**

1. **Users:** 

   - user_id (Primary Key)

   - username

   - email

   - password

   - shipping_address

   - billing_address

2. **Products:** 

   - product_id (Primary Key)

   - name

   - description

   - price

   - quantity_available

   - category_id (Foreign Key referencing Categories table)

3. **Categories:** 

   - category_id (Primary Key)

   - name

4. **Orders:** 

   - order_id (Primary Key)

   - user_id (Foreign Key referencing Users table)

   - order_date

   - total_amount

5. **Order_Items:** 

   - order_item_id (Primary Key)

   - order_id (Foreign Key referencing Orders table)

   - product_id (Foreign Key referencing Products table)

   - quantity

   - price

**Relationships:**

- Each user can have multiple orders, but each order belongs to only one user (One-to-Many relationship between Users and Orders).

- Each order can have multiple order items, and each order item belongs to only one order (One-to-Many relationship between Orders and Order_Items).

- Each product can belong to multiple categories, but each category can have multiple products (Many-to-Many relationship between Products and Categories, implemented using a junction table not explicitly shown here).

  

This schema provides a foundation for storing information about users, products, orders, and order items in an online merch store. Depending on the specific requirements of the store, additional tables or columns may be necessary.