The underlying Salesforce.com service in this environment essentially runs in the background as developers tweak buttons and interfaces depending on what's needed. The code underlying Visualforce ...

You can attach Apex code to Salesforce fields, adding new business logic to a process, so you can, for example, calculate delivery costs and delivery times based on a customer’s address.

Salesforce Classic isn't going away anytime soon, but that doesn't mean you shouldn't be planning your move to the new Lightning UI. Here’s a transition guide for the bewildered.