This is the code that is sent to the user when verifying the email address.
This records the users IP address so you can block abusers (i.e. Spammers)
This the email address used when they place the order
This is the name of the product ordered
This is the price of the product ordered
This is the SKU (Stock Keeping Unit) number of the product ordered
This is the quantity of the product ordered
(actually, what is the purpose of the order details table?)
This is called Database normalization. The order is separated into two parts. The first part of the order contains information about the order itself, while the second part (Detail) has a record for each item ordered. This allows you to have unlimited numbers of items for each order without wasting space in the database.
See this article for more information:
Designing a Database
Yes the vendors table is strangely absent but you can easily add it to the database following the example of the User table.