I can't Understand the difference between Order And Quote or Order Items And Quote Items please explain what is it and how it works
I believe this is very basic question. Though I will explain it in detail.
Quote/Quote Items :
When you click on "Addtocart" button from that time your session starts. Magento quote saves all your session data until you place the order successfully. Quote keeps all data related cart like all types of totals including subtotal, grandtotal, shipping, etc and customer details like firstname,lastname, email id, etc. While quote items table keeps record of individual items added into cart. Quote items table has data like product id, sku, name, price, qty, etc.
Order/Order Items :
Whatever the data available in quote and quote items table those data transferred into order and order items table when you place the order successfully.
So the basic difference is that quote/quote items table keeps customer cart data till customer places the order. Once order is placed those data is transferred into order and order items table and customer's respective quote becomes inactive.
I hope to have explained properly. Let me know if you have any more queries.