What are the basics of Visualforce and when is it still used?

Visualforce is Salesforce's tag-based markup language for building custom UIs. Key components: apex:page (root element, defines controller), apex:form (wraps interactive elements), apex:commandButton (triggers controller action), apex:inputField (renders a field with FLS enforcement), apex:outputField, apex:pageBlock, apex:repeat (iteration), apex:messages (display errors). View state: Stores the page's data between requests (max 170 KB) — keep it small by marking transient fields. Visualforce is still used for: PDF generation, legacy integrations, embedding in flows/layouts, and cases where full LWC is not yet feasible. New UI development should use LWC.