Introducing a Visualforce page
In Salesforce, it is very easy to build powerful applications using only declarative methods; however, there are some situations where declarative methods aren't enough if you want to build an application. In Salesforce, standard and custom objects have their own standard user interface, either classic or Lightning Experience. You can easily customize a standard user interface by creating multiple page layouts using "clicks not code." A standard user interface has its own limitations; for example, you can't create three column pages or generate a PDF out of it. This is where the Visualforce markup language comes into play.
Similar to HTML, Visualforce is a markup-based user interface design language. Visualforce is a framework that includes a tag-based markup language that allows you to build sophisticated, attractive, and dynamic custom user interfaces. You can use almost all the standard web technologies, for example, CSS, jQuery, HTML5...
