What is an object?
An object is an instance of a class.
All objects have state and behavior, that is, things that an object knows about itself, and things that an object can do. The state of a PurchaseOrder object—what it knows—includes the user who sent it, the date and time it was created, and whether it was flagged as important. The behavior of a PurchaseOrder object—what it can do—includes checking inventory, shipping a product, or notifying a customer.
Order__c orderObj = new Order__c();
here “orderObj “ is the object of the Order__c.