What is Visualforce controller in Salesforce?
 A Visualforce controller is a set of instructions that specify what happens when a user interacts with the components specified in associated Visualforce markup, such as when a user clicks a button or link.      There are three types of controllers available in visualforce. Those are:    Standard Controllers    Controllers    Extensions      Standard Controllers:    A Visualforce controller is an arrangement of directions that indicate what happens when a client cooperates with the parts determined in related Visualforce markup, for example, when a client clicks a catch or connection. Controllers likewise give access to the information that thought to be shown in a page, and can alter segment conduct.
Create & Use Custom Controllers
Prologue to Custom Controllers: Custom controllers contain custom rationale and information control that can be utilized by a Visualforce page. How Visualforce bolsters the Model– View– Controller (MVC) plan design for building web applications. Controllers regularly recover the information to be shown in a Visualforce page, and contain code that executes in light of page activities, for example, a catch being clicked. When you utilize the standard controller, a lot of, well, standard usefulness is given to you by the stage.















