'Customers' are simply contacts which have had an invoice generated.

If you view Contacts -> Contacts, you will see a view of all contacts (model: `res.partner`).

If you view Accounting -> Customers -> Customers, you will see that it is also a list of all contacts (model: `res.partner`), except with the "Customer Invoices" filter applied.

One question : how do you change a contact into a custumer ?

ok thx for your question customer and contact ofcourse they have different,let start by customer this a person or company that can make exchange of money and product;and then contact is it is communication betwen two person i think thx

Just explaining a little bit more on what has been already explained.

Both could be considered contacts, the only difference is tha one of them is related to a customer record.

I suggest you to refer to the responses Marked as answer in the following thread which discusses a similar issue.

Contacts contains customers, vendors, employees and all partners

So customers are part of your contacts but generally there's no technical or functional difference between both as you can use any in any system transaction with no restrictions

Every person in odoo, Customer, Vendor, Employee, all branches contact details is stored in contact 

As i observed that Your contact will be your opportunity,Customer,Vendor either its individual or Company and Customers means a goods or services which you have already supplied. 

In my opinion, Contact is the contact information of an individual, a certain organization or company.
And Customers are the people who directly consume the products of the business and generate profits.

Hi,

Contact and Customer are the same in Odoo where the model is "res.partners".There is no Technical difference between the two but there is a concept called customer rank,which decides whether a contact is customer or not so functionally there is difference between the contact and customer.

Regards